I just want to know this:

Can i join a server using mods which don't affect the car's performance, like sound mods? And will my game crash due to having mods and the other drivers don't?

Sound mods, new textures, stuff like that are just fine. The server won't notice them and you won't be kicked.

oh and your game wont crash either

Yah.. You can use ANY mod that doesn't give you an advantage.. hurt someone else, or cause troubles in the server.