SMK works quite differently than the rest of the series when it comes to drifting. For most longer turns it's much better to hop hop hop hop instead because as I think you've noticed you will spin out if you drift for too long. Hopping resets the drift so you wont spin out as fast.
Counter-steering when coming out of a drift is also an important technique which lets you align your kart much faster after taking a tight curve. Just turn in the opposite direction of the curve for a split second before letting go of the drift/hop button. It can take a while to get it right but it's a very neat trick.
I also highly recommend using Koopa Troopa or Toad as they have the best handling in the game and handling > all in Grand Prix.
I tried to find a good video on youtube demonstrating this but couldn't find any. If you still need help I could record one tomorrow or something.
As for the moles; you can shake them off by hopping.