1) How long did it take you to reach 25 subs? 100? or even 250 (for tipping)?
If you're talking since the first time I uploaded on Tapas, I would say 1 or 2 years - I didn't know what I was doing at the time, and my comics generally weren't very entertaining.
However, Catma managed to reach 250 in a few months or so. This success carried on to Project SHaDe, of which I am happy to say is going quite well. (Though, I would lend its success to the generous Tapas team that have promoted it twice now - I would still be a tiny fish without them).
2) Does publishing on a certain day at a certain time really determine views/reach? What time of the day do you think is best?
Not completely sure, but I would say it is best to post during the noon at least once a week.
3) Do you think art quality/skill matters?
Of course it does! Comics are a visual medium, and you should take full advantage of that.
At most, focus on readability, composition, and general appeal. The last one I can't really help with, but the first two are things you can study by looking at other successful comics, both amateur and professional.
Mob Psycho 100's success proves that you don't need to be extremely polished to hook readers in - what matters is that you successfully communicate with utmost clarity.
4) Why do you think your story is doing well on Tapas?
Other than having been promoted on the home page twice now, I'm not absolutely sure on what makes Project SHaDe successful.
One thing that many readers point out is that they enjoy the sketchy aesthetic of the comic - in that sense, I would say the visual appeal is a large factor in the comic's success.
Others have also said that they enjoy the quick pacing and the gruesomeness - some have even pointed out similarities to Tokyo Ghoul (I damn knew they'd notice that - it was difficult to hide my inspiration).
In that sense, I think it's important that you make something that appeals to you fully - more often than not, your appeals stem from media that other people enjoy. This will seep into your own work, and said demographic may also find interest in your work.
5) What if I have a good story but I'm not getting views, what should I do? (plus I don't have many social media followers less than 500?)
Post often, as it keeps you on the fresh page for longer - you raise your chances of being read, and if many people begin to read it, your comic may end up on the trending section, which will be extremely good for you.
Advertise yourself in various places too. I haven't tried it myself, but I've heard subreddits for webcomics are quite good for getting yourself out there.
6) What did you do to get noticed? OR How do you think you think you got noticed? (this is great for those that got a surge of subs in a day, but if you didn't that's fine too)
I got noticed by making a whacky but appealing one-shot (Catma) - this drew readers in, and gave me a good foundation of readers to start the next big project I actually wanted to do (Project SHaDe).
I also eventually had Project SHaDe placed in the spotlight, which drew in a humongous number of readers for the comic. Even now I am still astonished that Project SHaDe even reached that point.
7) Free question: Was there a question you wish you could find the answer to when you first started out but you have the answer now? Then drop that here. There may be someone asking that same question and you can give them the answer
The question I wanted would have been: What is the best way to start?
My answer would be: Start small. Make a one shot of 30 pages or so - something imaginitive that will appeal to a good number of readers. Keep doing this until you both have the skills/confidence to pull off a larger project, as well as a large readerbase that will jump on that ride.
8) Any other advice I should keep in mind?
With your comic, know how you're going to end it and have a grasp on the scope of the entire project. This way, you won't get overwhelmed after realising you've taken on a responsibility that you can't keep up with.
Also, make something that is emotionally honest. It may be reliable to draw a comic that follows the formula of something popular (e.g. Coloured, vertical scrolling, webtoon-esque aesthetic, Romantic Comedy etc.), but it is not use doing them if the only goal is to gain some emblance of popularity.
These elements aren't inherently bad, but you shouldn't do them for the sake of gaining a readership.
If your project is emotionally honest, you at least won't hate yourself for continuing to draw it.
I hope this helps!