100
There is sonic, tails, knuckles, amy, rouge, eggman, shadow, chaos zero, tikal, dark chao, normal chao, metal sonic. So that would be 12 characters.
Nine levels
Quite a few, the most knowledgeable ones are. Sonic the Hedgehog 1, 2, 3 and 4. Sonic and Knuckles. Sonic Spinball Sonic 3D Flickies Island Sonic Spinball Dr. Robotnik's Mean Bean Machine And a few others that can be found on Sonic Mega Collection Plus. Sonic CD Sonic the Fighters Sonic R Again, more can be found in Sonic Gems Collection Sonic Shuffle Sonic Adventure 1 and 2, including the DX and Battle additions. Sonic Heroes Shadow the Hedgehog Sonic the Hedgehog 2006 Sonic Unleashed Sonic Colours Sonic Riders Sonic Riders: Zero Gravity Sonic Free Riders Sonic Advance 1, 2 and 3 Sonic Rush Sonic Rush Adventure Sonic Battle Sonic Rivals Sonic Rivals 2 Sonic Chronicles the Dark Brotherhood Mario and Sonic at the Olympic Games Mario and Sonic at the Olympic Winter Games Sonic and the Secret Rings Sonic and the Black Knight Various arcade games. And many more that aren't mentioned here.
five
Sonic:6 Shadow:4
yes you can find it in many levels
21
You need to have at least iver 25 emblems to get a green egg in sonic adventure 2 battle
170 or 180
There are 21 animals
100.
100
20
50 or 40
100
Yes and no, They are going to make many new sonic games and Sonic Unleashed was origionally going to be named Sonic adventure 3, but I think in 1-3 years should bring it along. Besides, the Sonic Adventure series contained the only two "good" 3D sonic games. I am sorry buddy, but there is no definite date