A: Yes, these can be placed over an existing stair case.
A: You can put the finish on before you install the treads.
A: A retro stairnose is available through you local store. The stairnose is 3/4 inch thick to accept 3/4 inch thick flooring.
A: I am only finding the red oak landing tread, not a white oak version. Is there a white oak version available? I need the species to match.
A: You do need a very good 12" saw that cuts straight. They usually start in the $300-$600.