Suntour made great RDs, steel or aluminum. The Deore will wiegh less and take up more chain but not work that much better. Rebuilding a bike is a job in cleaning and greasing. The BB that came with the bike just needs to be cleaned and greased/adjusted. I think that cup and ball BBs are better then cartridge BBs, but it depends on quality and money. For your BB buy some new ball bearings 1/4", check the cones for pits. If the cups are pitted then you get to look for a new BB.