can you have multiple characters on one account? and if you can, does it add to the monthly fee? i dont actually own WoW but my sis' boyfriend does and i want to create a character on his account instead of messing with his...you know the whole "why did you do that? i dont want that spell wtf?" situations? i'd like to avoid that.

Yes, WoW is pretty generous with the extra characters on one account. No extra charge. Technically you can have 8 characters on every single server. So that is a hell of a lot of alt characters. Technically however it is against the EULA to have more than one person using the same account. Well regardless enjoy... I love WoW and don't let the haters get ya down.

I believe the limit is 60 characters over all server as well.

I had no idea they had a character limit for all servers but then again who would really have 600 characters.

I have a friend who has like I think 8 characters on like 5 servers I believe you can have that many on as many servers you want.

You can use one account and even one server with multiple people. As long as you don't play at the same time, it should be fine.
When your friend logs into the game, while you are connected, then you'll get disconnected.