• The game will be a four-button fighter, with the other two used for special functions. Two punch buttons, two kick buttons, a button to dodge/block, and a throw button. It will not be based on Sonic Battle. We already have one of those.
• The game will use advance-style sprites. Custom sprites and sprite edits will be used when no suitable sprites can be found
• The game's roster will consist only of official characters that originate from the games. That means no Sally Acorn, no Scratch or Grounder, and no Ashura.
• The game will be released as a series of betas so that the general public can give report bugs and give constructive criticism.
• As for the roster itself, the game will attempt to incorporate both older characters and recent additions. I will attempt to incorporate most of the popular or major characters with a few minor characters and fan favorites.

Blaze, Silver, Espio, Omega, Metal Sonic, and Mighty.

Well, I've already found an Omega sprite sheet, but now that I think about it, it doesn't fully adhere to the style. Maybe I'll just put in Gamma and have Omega be low-priority, if I put him in at all. Trust me, people will notice if I just use Gamma's battle sprites and call him Omega. The feet are not the only difference by far; Omega's hands are longer and silver-colored, his body is shorter yet wider, he has bulkier shoulderpads, and his eyes are red instead of green (though the last one can easily be fixed).

As for your concerns about advance-style sprites, I've managed to find several sheets that fit the style almost perfectly, though you seem to have a much more critical eye than I do, so I don't know if all of them fit your standards. I'm uploading some of them to the forum, actually. You can check them out if you want.

So far, I've managed to find some good sheets (with plenty of poses) for Blaze, Silver, Metal Sonic, and Espio. The only problem is that none of them have enough poses for the project, so I'm going to have to ask the permission of the original creators. Blaze, however, was actually edited from official pixel art that was played over the credits of Sonic Rush, so making poses directly from the official sprites wouldn't actually be unauthorized editing.

Still, it'll be a while before I get to the point where I start to have to use custom spritesheets. Right now, I'm just focusing on getting Beta 1 out, which will only have 4-5 characters straight from Battle.