Osb is not usually a recommended subfloor for nailing. Why not consider a floating floor of engineered wood? As far as the environmental issues goes almost all oak or major hardwood lines reforest and use environmentally friendly harvesting. Some exotic woods may not. I wouldn't worry about that aspect as much.

"He told me that 99% of the time they can be re-finished with no problems even if there are pet stains." Stains often sand out, but if the satin got between the strips it may not be possible to sand deep enough to remove everything. "How many options are there for staining?" Probably millions. "I'm not sure if it would be easy to add additional floor boards. " You can often steal matching strips from closets, though obviously they will all be shorter pieces. 1957 wood should not be that hard to match. It is unlikely to be old growth with very tight grain.

Boxers is right...It might take months for the moisture to leave the wood and for the floor to regain what we call equilibrium. After the floor has stopped settling back down and moisture readings are constant across the entire floor, then you can consider resanding, if that will even be needed. I too recommend an evaluation by an expert after the floor has had sufficient time to normalize.

"Tom Silva replies: You can do it either way. My painting contractor, Jim Clark, wants to be last so doesn't have to repaint baseboards that have been splotched with stain or ployurethane, or nicked by a sander. Besides, even the most careful flooring contractors inevitably leave a film of dust everywhere, he says. My flooring contractor, Pat Hunt, sees things a little differently. He prefers to be last because floor finishes take a while to fully cure, so he doesn't want anyone walking on them even when they're covered with protective tarps. He also says it's pretty common for other contractors to damage or spill stuff on a finished floor. The way he figures it, it's much easier to touch up paint than a floor finish. As the general contractor, I sometimes have the flooring finisher go first, and sometimes I let him go last. It all depends on what's best for the project schedule. I have that kind of flexibility because I know Clark and Hunt will put a lot of effort into protecting the other guy's work." https://www.thisoldhouse.com/ask-toh/what-comes-first-wall-painting-or-floor-refinishing