by getting good times on each track.
Get gold trophy in grand prixs to unlock karts and characters.
Rob is not in Mario Kart Wii.
You do an amount of races or you can finish cc's.
you have to complete certain things to unlock stuff. this website shows you how to unlock everything, including karts. http://www.videogamesblogger.com/2008/04/18/how-to-unlock-all-mario-kart-wii-secret-characters-bikes-karts-and-more-guide.htm
Complete the first stages
You have to unlock one expert staff ghost in time trials
Simple, you don't, you unlock baby daisy.
You have to unlock 8 expert staff ghost data to unlock him
Sorry, I dont think giga bowser is a character in Mario Kart Wii.
you have to unlock the different karts by racing the world cups.
Complete the Mushroom and Flower Cup.
Play 16 time trial races.