No, but I do believe a Chao does make a cameo in Sonic Rush when you are about to play 2P with a friend.
Well,it's 50:50,none can really say.
You beat Imperator Ix up on Angel Island and Shade realizes she was being used. She betrays her entire clan(and I believe she and Knuckles have a crush on each other!)
Yes, infact Sonic has been in three games with Mario in them ( Super Smash Bros. Brawl, Mario and Sonic at the Olympic games, Mario and Sonic At the Winter Olympic Games) and one with Zelda and other characters such as Spyro and Snake and such.
If you mean by any other type of sonic games,yes in sonic rival 2
Simpsons Game, sonic unleashed, other sonic games
Both Sonic and Mario have appeared in Mario and Sonic at the Olympic Games and Super Smash Bros. Brawl.Some people have hacked other games to make Mario look like Sonic.
knuckles in sonic two, blue sphere, sonic 3 and knuckles, flickey and ristar.
Yes, Espio is from sonic he was made for knuckles' Chaotix. he also appears in various other games related to sonic.
sonic mega collection plus (sold sepretly or in sonic PC collection which has 3 other games which are sonic riders sonic heroes & sonic dx director's cut
Either play the games lots of times or play them for many hours. Also having other sonic games on your memory card will unlock some games.
sonic (2006) for sure but besides that, sonic and the secret rings or, otherwise silver is not in many games at all, so i do not know, you might need to find out other games he is in
Mario and Sonic at the Winter Olympic Games could be considered as Mario and Sonic at the Olympic Games 2, which would mean that the game is already released. Other than this, Mario and Sonic at the London Olympic Games will be released later on this year for Wii and early 2012 for 3DS.