Well let's see, use the spin move a lot if you're in a jam or if you can't quite make it to the next platform. Go around the level in a clockwise fashion - but leave enough space at the beginning so that you can get back to the starting platform to get the star. I didn't find the time to be a problem actually, just everything else. If you've noticed, the area all the way in the back right is loaded with the most coins. What I do is make my way around to the extra life, then line up to long jump over to the back right corner. From there, there are two lines of coins you can get by long jumping across to a section of yellow blocks and then long jumping back. If you manage to make it that far, you can hunt around the middle and near the starting platform for the remaining 10-20 coins. Good luck. It only took me about 5 million tries!

As for the dreadnought garbage blow up star, you go in a pipe on the underside of the platform you start on.