On bare pine, I'd use 3 coats. In warm dry summer weather, a coat can dry in a s little as 2 hrs.How many coats do I need to apply? And is this only if I use something like pine? Will there be an issue if it rains between coats?
In high humidity, it could take 24 hrs. On rainy days, it might take a bit longer.
Sand lightly (just enough to knock the grit off) between coats. Last coat won't need sanding.
Use a fine sandpaper, like 200 or more.
Rain will only be an issue if it falls directly on what you're finishing. I do mine in the garage.