Oh my god I did this with What is the Price of freedom before I decided to make it in a full story as well as its counterpart which is another "one-shot" called Lacrimosa. The entire prologue was something I wrote along with Lacrimosa. But it was so, well liked by a lot of people that I turned it into a full series x3
Way back when I first began dreaming up my own stories, I had all sorts of epic storylines which never saw the light of day because they all involved trudging through reams of introductions and expositions before getting to the 'fun part'.
My first 'proper' completed story was a submission for a comic magazine seeking 20-24 page one shots. I took an idea I already had about reimagining the Demigods of Greek Mythology in the present and after some cutting and distilling, made Ti Amo2. Like others in this thread have mentioned, the experience was a great starting point- I learnt the importance of engaging readers from the get go, focusing on relevant plot points to keep things moving along, and the responses I received gave me the push and confidence I needed to make Pandora's Scar1 -my present full length series.
So short stories doesn't mean abandoning epic ideas, just arranging them in a more manageable format so you can well and truly get into it and have something concrete to show for your efforts 
Since we were chatting on the other thread, I'll pop in here too!
Getting from that initial concept to the full story/script is definitely super tough, but here's the process I took (which may or may not work for you, since everyone has different work flows xD)
Right from the initial concept (when I had my characters/general idea down) I worked out what I wanted the main 'conflict' of the story to be. The shorter the story, the more important it is that you have this part nailed down, because it kinda sets up the pacing for the whole thing. For example, a comic that's 10 pages long doesn't have as much room for build up as one that's 50 pages.
After figuring out the conflict, I took to bullet pointing out the major events of the story. Very little detail or exposition, but just getting the scenes/plot points down on paper. I started with "beginning", "middle" & "end* and then interpolated from there. Since I knew who the characters were and what I wanted them to accomplish throughout the story already, this was made easier. I knew roughly how the story started and how it was going to end. Filling out the middle was the hard part, and took the most time. But yeah!
Next I took my bullet points and wrote them out as like full paragraphs, in like a loose novel format. I guess this is the closest I got to "scripting" in the whole process, although I pretty much left out all of the dialogue, focusing more on describing how the scenes played out.
Editing down came next. I knew from the outset I wanted the scope of the project to be ±50 pages, and reading back over what I had written I knew I would go wayyyy over that. So I started trimming the fat. I had a bunch of largely unimportant characters, so I cut them out. Removed some of the fluffy in-between scenes that did little to advance the story, etc. All things that would have been at home in a lengthier comic, but had no place in this little one-shot.
Finally, I opted to just storyboard out the whole thing instead of doing a formal script. This took like 2 and a half weeks, but was super valuable for me! I'm more of a visual person than text-based, so it was easier to get a sense for what happened in each panel and who said what when and where by just sketching it out. Further editing down happened in this process too, as I got near the middle of the story I realized it was progressing too slow/taking too many pages so I had to adjust some things on the fly. When all was said and done, the story came out to 66 pages. 16 over my goal, but I didn't feel like editing it down anymore, so that's how it ended up xD
For an example of what my storyboards looked like/quality wise (really quick/sketchy):
But then having that has made drawing the real pages easier since I know roughly the expressions and where the text goes/how much of it, etc. Here's how page 2 finished looks for comparison:
So yeah! Def don't rush it and be sure to take ample time to plan the story out, since it'll make things easier down the line 
part of what's scary about long comics is that a lot of people (myself included) don't do enough of that planning before jumping in. Even just having a general bulleted list of events and then doing the other stuff chapter by chapter is better than going in blind xD if/when I ever get back to my long story, that's probably what I'll do. The planning for this comic was a massive learning tool though!
I have a couple one shot series and while it doesn't really bring in the subs, it will help you write/make longer pieces.
I can confidently say i've completed a couple 2k words, 3k pieces so 7k is kind of a joke for me now, but now I'm pushing myself to finish a 12-15k series now. Last year I couldn't even get to a k in a day.
DUDE! AMVs! I USED TO DO SO MANY OF THOSE. I often picked Avril and MCr because i am a True Emo at heart and I love angst.
Bro if you still love that story literally half a decade later it's pretty safe to say you won't XD Will you be following the rp storyline pretty hard or will you make use of your creative license?
The latter ones are the most daunting, tbh. I. Uh. I can't seem to let go of ideas. But yeah, I should probably do that. I can't seem to sit still for a month, though. I keep worrying about ideas not being used 
Why yes, yes I am going to reply to everyone. Tapas says to reply to several at a time, and I see their point, but I'm like. Nah.
There it is, the exact reasons why people should do practice pages first You're the first one here though that said u started on fancomics instead of one-shots!
It really doesn't huh. But yeah, putting in the time seems to be the general consensus that it will help you in the long run
Highfive! Hmm..dont think I heard of MCr but I often used Disturbed or Hard Rock in general so pretty angsty stuff as well lmao. I still have them up , even though they all look so embarrassing now and I am probably the only one getting the context of the scenes lol.
And yes we are following the RP story for the most part, especially the major plot points. The changes are mainly on the world building stuff because we can't use the lore of the game we were RPing in. We had to make it our own world. Also we changed or added some events that made more sense in the grand scheme of things, knowing where the story is gonna go. Sometimes in RPs, there were spontaneous moments when a character does something with barely an explanation or just to be silly and the next thing we know that small action had a huge impact lol. In the comic, we have to back that action up with something that made more sense instead of this character just trolling the other (for example).
Sorry I tend to ramble. lol
that is a ton of useful info and yeah, useful for me, but i dunno about the others XD
