you pulled off the carpet and pads and saw a virgin hardwood flooring. It could have been a nightmare, as you are aware of.
Being covered for so long, the dryness and such has dried out the wood and its lost alot of luster, oils, and protectants.
These all can be easily restored.
What I would do is to completely re sand the entire flooring. Since you are in good shape, forgo the coarse paper and begin with medium and work gradually down to steel wool.
When the flooring is sanded and smooth to your liking, I would add a good stain product with oils to enrich the dried wood. This should remedy many of your small cracks. The oils and moisture should swell the wood to an extent for a good and tighter fit.
Do some consulting of a floor specialists also, but you can do the actual work.
You can rent all the machinery needed for the task.