From what i understand, Rosalina should be unlocked if you have a mario galaxy file saved on your wii.
I cant wait to pick mine up tomorrow, Im in the States, so I dont get it until then. Dont worry though, I'll be on the leaderboards soon enough

. Same name you see on the forum.
The blue shells always affected other racers, not just in the wii game. If you were close enough the explosion hit you. Also in the N64 version, it could smack you as it flew by. I know its dodgeable in Double Dash version, but its so hard and alot depends on luck.