You got 400? I got 40. I don't mind the pit stop at the moment. They mentioned that you will get bonus wumpa coins when the seasons start and I am not really into buying all the stuff at the moment. Like I mentioned before if I finally beat all time trials I probably will end up with all the coins I need because the times are so hard; N' trophy is doable. Controls/online I have no issues but I would not mind if loading times would be shorter :p.
You get more coins from online multiplayer races. This reddit post explains wumpa coins quite well.