get 1st place in all the other races and i would recommend Yoshi to race with (just to unlock stuff though)
by getting gold on the star cup
there is no hat cup
By finishing the race's
Beat the star cup
You have to win first place on 150cc Special Cup
You have to come in 1st place on the special cup in 150 cc.
You unlock star cup by by winning any cup in the flower cup in the respective class you want to unlock.
Unlock the star cup and play it.
Quite easy. Just beat the 50 CC Star Cup.
To unlock the quaker you have to win 150cc star cup
You have to do the Flower Cup, and the Mushroom Cup.
Well you need to try to get first in every race/ cup there is and try and get gold to unlock more karts, bikes and chars