Hello. After two days of hardwork, I completed sanding the hardwood floor with the a rented U-Sand. Going to apply the Minwax water based oil modified finish. Not going to stain. However, before I begin I have two questions which I'm still not very sure about. 1. There are some small spots (dents, low areas, edges, corners, etc) where the old Oil polyurethane is still there. I can remove those with my detailed sander and hand held random orbit sander. But there are a lot of those spots, it is time consuming work and I might miss a few. I know it wouldn't look as good, but would there be any issues if the new urethane is applied on top of them? 2. Originally I was going to use tack cloth to wipe clean all the dust once I sweeped and vacuumed, but then I found out tack cloth might leave wax residue behind that will screw up the Urethane. Likewise, Mineral spirit can apparently stained the raw hardwood (and I'm not sure how it will react with the old left over urethane spots). What options do I have to get the last bit of dust out? Would buying bunch of microfiber cloth and wiping the floor with them work? Thanks.