Go check out the Minwax website for lots of info. Yes, you need to remove the wood and sand it. Unless you're trying to get out real deep scratches #220 grit or so should do what's needed. Go slow, go in the direction of the grain, and you should be fine. You need to stain before sealing the wood. You can mix stains of the same type, oil or water, you'll just have to mix enought for the entire project and make sure to test for color. Tru-Oil is a oil base finish, not a sanding sealer. Try to stay with either oil based or water based products.