Y'know, I'm gonna delve again where Hukuna and Stratos have already touched down upon with their artisan hands. Frankly, I've never had the street smarts when it came to making RPs, although I behold the book smarts, which is a harsh duality when I think about it. It's the lack of experience from running these things where I cannot speak on an accurate first-hand basis compared to the seasoned members of this subforum.
I represent a different end of the spectrum when comparing myself to Huku and Strat. Where they are the more analytical type, I'm willing to roll with the punches and accept what comes, as long as it's within feasible logic. Mostly everyone here likes to write straight and to the point, and maybe not elaborate on it spectacularly like Hukuna and Stratos. I've seen them both critique various pieces of work, and it's really harsh to, honestly. I feel like I'm already following in their footsteps since I'm now in AP Literature and the biggest goal of the class is teaching us to craft and analyze the structure of any written or typed piece of work and pick it apart, like Hukuna does.
Tyran, while I will agree with Hukuna and Stratos that you should definitely polish up on Battlegrounds, I will advise only on certain parts of it. Part of the craft of storytelling, even in RPs, is occasionally leaving certain aspects to the reader's - not the author's - imagination. The 6 arcs of kingdoms to follow and max of 6 characters was definitely excessive, and you haphazardly throwing in the "important" details, for instance the philosophies of each kingdom. That's where you need to leave it to the imagination. Maybe the Sky Kingdom thinks of superiority since they fly higher, both metaphorically and literally, above everything else. Maybe Underdark is plotting for domination because they were cast into the murky abyss of the underground and it's time for them to rise again.
It's the thought that counts Tyran. I followed this RP almost sacreligiously, because it was well crafted under the Sky Kingdom arc with Yash and Stratos (who I knew as Wander then) at the helm. I crafted my posts as excellently as I could, because I knew then, those two were the bar I personally needed to set. This is the RP I put the most thought into when considering my characters so far. This is what has tested my mettle and sort of helped me become a better writer, through the analysis of others' posts.
This was a great idea, please don't let it go to waste. I made Sons of Nalin as a substitute for this, and I'd be willing to even take the keys Tyran if you wanted me to. I thought this RP over well when it was in session, and now it's all flowing back.
EDIT: To answer your questions.
1. Three kingdoms was good enough, and six was a little overextending. Since we have such a shallow pool of RPers, let alone those willing to participate, I'd actually vouch for no more than 3.
2. Don't really care since the only real fighting done so far was the fighting in the fields I can no longer remember the name to that belonged to no one then.
3. Backstories are what I'm hearing. If they assist you in worldbuilding, then by all means YES.
4. Still gonna go with my earlier suggested limit of 2 characters per player. It prevents the stretching of resources, which even at 2 with my Alucard and Ulkina, I kept them together to make it easier, since it made the story for the 2 of them simple to follow.
Hope it helps.