1. Why can't you reverse the slings? Not sure I understand the issue, but whomever installed the hoist should be able to make adjustments for your boat, if you can't yourself.
2. This keeps the boat dry, but a foot and a half difference seems extreme. Again, this can be adjusted. You also don't need it 5' out of the water, just out of the water.
As far as hurting the boat, that's pretty much nonsense. As long as the slings are clean and debris free, you will be fine. We stored boats at our cottage on a hoist for over 20 years without issue. One of those boats was a fairly large and heavy open bow.