Sonic Crackers was a test rom to show off the ring system from Knuckles Chaotix and has simular sprites to Sonic 2 if I remember correctly, been some time since I last played that game. Many Sonic Crackers remnants, such as Tails and Sonic's colours still exist in Chaotix, and Mighty from Chaotix is actually just an edited Sonic, as is obviously shown by that Sonic Arcade game with Sonic, Mighty and Ray (A flying squirril who never once appeared ever again)
And don't put many characters. Stick with the classics and the cool ones. Sonic, Tails, Knuckles, Robotnik, Metal Sonic and maybe Nack the Weasel/Fang the Sniper. He was awesome. And possibly Mecha Sonic as well, though Metal has a personality and Mecha doesn't. And perhaps Amy, though she doesn't do much