This is the reason I haven't finished The Wheel of Time series (which I started reading 20 years ago) and ooooh I've tried. Every time a chapter with a character I just don't care about (or even remember in some cases) came up it was a struggle not to drop it and one that I always lost eventually.
Glad you asked. Currently, Amazement Comics has 250+ characters in its entirety (though the number is subject to change). That's why I created a series on Tapas that is more or less a character biography series. I don't know whether or not we'll get around to all characters, but we want to get through most of them. Perhaps all of the main characters, because there are many stories, involving many different people, that requires their OWN main cast apart from the rest of the OC's. The minor characters are exactly what they sound like. So I don't use them often in the stories, but I have identified every possible main character, and minor character out of everyone that exists in the whole fictional universe.
The worldbuilding in the comics is relative to who is a main character and a minor character. So I would suggest creating a character guide series like myself, or making outlines of your characters and saving them to a word document.
This is a big worry I often have. I think it's more common in novels that comics, since comics I can at least recognise a character by their looks rather than just a name like novels. Even if I don't know their name it's yeah the the redhead one. Of course this gets trickier the bigger cast, but this is why lots of visual medias have characters in just one signature outfit.
To be fair, I made it through thousands of pages before I couldn't stand it anymore! I think it's only an issue in a long-running series where you're juggling more than a dozen POVs and introduce more pov characters late. I mind it a lot less in novels where we stay in one person's head (or just a few).
Yeah, too many POVs can be a nightmare, especially if they don't have distinctive voices. I always try to stick to no more than 3 but mostly I'll stick to 1. It's just easier for everyone.
I write my novel in a sort of omnipotent third-person perspective because I have the easiest time writing in a script format, so I like having the freedom of being able to shift the mind's eye to whatever place I want it in the scene. I rarely get inside a character's head and generally like to just show things happening. I do have quite a few characters, but they're all pretty quirky and distinctive from one another.
For me I sort of have tiers.
There is the main tier. This where the main characters and the most important side characters go. They will have the most development out of the characters and appear more frequent.
There is 2nd tier. These characters will appear briefly and have some importance to the overall plot. They might have some background but it's not as deep as the main tier characters.
There is 3rd tier. These characters appear rarely but have some importance. These characters tend to have little to no depth but usually their to fill a role. For example, a character's parents might appear here.
Then there is 4th tier. These are mostly just characters to fill space. They might have a brief speaking role but has no bigger impact on the overall story. Some may not even have names.
I think the thing some people might find overwhelming with a large cast is when a creator feels the need to put most of the characters in the main or 2nd tier. Not all your characters need to have a deep backstory. If a concern is "I have too many characters", I would recommend combining similar characters and/or cutting pointless characters.
I have seen so many even professional creators fall into this trap. They constantly introduce new groups characters with fully fleshed out backstory and details when a previously introduced character would do the job just fine. An entire new group of villains with names and backstory to be killed off 2 chapters later when you have perfectly good groups of mooks running around already. And using fully fleshed out characters when faceless mooks will do the job. I don't need to know the redshirt's life story.
I have a pretty large cast of main characters, along with a bunch of other reoccurring characters. I have my main characters set in tiers: My MAIN main protagonists, main antagonists, other main protagonists that have important parts in the story but aren't necessarily introduced right away, and supplemental characters who contribute to the story but not enough to be considered the main cast.
I really try to write my story intentionally, making sure every character interaction has its purpose and moves the story forward. If there's anything that seems like 'fluff' that helps build the world, it usually means that those characters will serve some sort of importance later on in the story. I also really try to develop my characters so they're multidimensional. I want them to have their own unique struggles and battles within the story itself that make them more interesting and memorable.
I always come back to Mad Men when I think about this. They had the main characters that got a lot of screen time like Don Draper and Peggy Olson, but they also had a ton of supporting characters who had their own sort of 'arcs' within the series.
My comic has an 8 character cast. I manage it by using a braided narrative structure. So each episode focuses on a different character. Over time the different separate stories for each character begin to cross over with each other. Conflicts and affinities between characters form and drive forward the plot. My mission with each update is to accomplish at least one of the following:
This allows me to tell an overarching story with a lot of moving parts and perspectives while doing my best to keep things coherent. This also means that a reader has to commit to reading probably a good 7-10 episodes to really know what the story is. So there are definitely pros and cons to this approach. I'm committed to a couple years of updates to tell the whole story though so I'm okay with the slow burn pace of things.
I consider a "large" main cast as five or more featured people. My series has a large main cast of six, now seven "main characters".
This is really good advice. I break my characters' interactions into smaller groupings. It's a lot easier, at least in my opinion, to weave together a bunch of short, cut scenes featuring 1 or 2 characters rather than showing the featuring them together ALL THE TIME.
My advise for larger casts is that if your characters don't know where X character is, YOU should. If the character isn't immediately involved in what the rest of the people are doing, we should know that they are off doing XYZ -- and if you can, show us what they're doing. It's helpful for subplots as well as explaining why someone disappeared for X chapters.
I also encourage that if you're going to name a character, they should have a "job" in the story. Sure, it's one thing to name a character if they have dialogue and interact with other characters in a scene. But if Terry the guy from the best friend's gym, has one scene, I'd say you're okay to refer to that character in "general terms" if needed later in the story. I've had trouble keeping characters straight if all there is, is a list of character names.
Cop shows or crime procedurals do an okay job with larger casts. Everyone who is featured regularly has a key role to the story and they don't add in new players without solid reasoning.
I think yeah small groups is really important. Even irl, even if you're in a large group gathering (which you shouldn't be right now obviously, stay safe people) of family or friends, you still generally only having a conversation with one or two people at a time, even if there are dozens of people in the room.
Very much this. You're allowed to call the mum who's just there to say hello and goodbye and little else "their mum" same with their teacher or boss or that checkout girl. They don't all need a name (I think it's a bit weird when characters call their parents by their names in close POVs).
I've never noticed this before but yeah, now you mention it. They're all in their lab/office/desk or doing their job. They tend to work in pairs at most and report to a single boss. They're very rarely all together cluttering things up.
I avoid it. My first novel had multiple POVs and large cast, and as much as I loved it, I wrote the rest of my stories in single or dual POV with limited casts.
Exactly. The main cast always fills a role like a protagonist/leader, love interest, muscle, the boss, the mentor, tech guy/genius, "hot one", etc. They might play multiple roles but once a character is introduced as a love interest; they're going to stay the love interest until the character is fully replaced. New love interests might get introduced but they'll always leave because the OG love interest is still around.
Characters are introduced as they become relevant. However, i sometimes drop hints of their existance by making early cameos in the background or foreshadowing.
I separate the main cast from the secondary cast, and in my current book/comic, I put the main cast in detention and everyone else went on a feild trip. Problem solved.
At the moment I just have four to deal with, but a do have a couple more of the main cast to add. I am not going to deviate away from the MC's POV unless it's absolutely necessary.
If it happens in a book I'm reading I'll just skip a few pages or skim read until it gets back to the main character's story line. 
Drawing-wise, I imagine it's a nightmare to cram all the cast into one panel/page. They did ok in End Game though.
My previous comic Zenchav had a large cast past chapter 9 and changed PoV a lot because I wanted to tell multiple sides of the story, thinking I could write it more like a book. It didn't work well because of webcomic update time, since if you shift PoV you're not going to revisit the other PoV for potentially years. If readers were attached to the original PoV...well... You've lost them, lol.
With my reboot ( Ring Spell) I've made the main cast more of an ensemble cast where the main four are almost always present, and the PoV never really shifts away from them. The plot (showcased through their interactions) is always driving their actions so there's not a single scene where the story isn't moving forward.
