Keep playing!
You have to play Time Trials on all courses to unlock toadette!
Not that I have heard of. Sorry.
i don't think you can only if your friend has Mario kart ds
Win 1st place on the courses you already have. They'll unlock the next ones.
Do a time trial at least once on all courses
Make a ghost on all of the courses in time trials.
To get new courses, you have to unlock cups (2 in the nitro and two in the retro) by getting gold trophies in the starting cups. After you have unlocked all the cups in 150cc and gotten gold trophies in them, you can unlock Mirror (known as 'extra mode' in Mario Kart 64), which is flipped courses in 150cc mode.
No you can only unlock more courses on single player mode.
there is no goomba to unlock in Mario kart wii
Play Time Trials on all 32 different courses
Play 16 different courses in Time Trials mode