i sand and refinish wood floors for a living and it sounds to me like all your bandaids might cause you extra expense when sanding time comes. the more oil,finish,paint or whatever is on your floor is part of what the cost is based on if the finish is worn off your floor as long as the wood isin't rotten just leave it alone and have them sanded as soon as possible. your black stains are most likely caused by pet urine . these will lighten somewhat when sanded but they may be to deep to sand out in which case you'll have those boards replaced which is no big deal. DON'T use any wood bleach on the spots, i've tried it on different things and it has always left a white bleached out ring around the spot when sealing and it never dit take the spot out.