I am near the end of having a 2 BR apartment remodeled in a building that I
own. The 2 bedrooms had old wall-to-wall carpet in them and I took that up.
The living room had a Pergo laminate floor in very good condition, but I had
to take that up because the remodeling changes resulted in the Pergo no
longer covering the full size of the room.

What I am now left with is 2 bedrooms and a living room with old red oak
hardwood floors in mediocre shape -- there are paint splatters and
oversprays on the floor, some pieces would have to be replaced or filled in
with hardwood (where closet walls were, etc), and there are some gaps
between some of the existing hardwood boards.

So, I am thinking my choices a

1) wall-to-wall carpeting throughout;
2) new laminate/Pergo-style flooring throughout;
3) replace the missing pieces and fix the existing hardwood floor, then sand
and refinish it;
4) add all new unfinished red oak (or similar) hardwood flooring throughout,
on top of the existing hardwood flooring, then sand and apply finish coats
of polyurethane, etc.;
5) add all new pre-finished red oak (or similar) hardwood flooring
throughout, on top of the existing hardwood flooring, and then maybe add a
coat of polyurethane to seal the cracks between the pieces.

The 2 bedrooms, living room, closets, and small hallway area add up to about
440 square feet. If I do add a whole new hardwood floor on top of the
existing one, that added 3/4-inch plus underlayment in floor height will not
present a problem. I have a person who can do the work regardless of which
option I end up choosing. I have been reading, researching, watching
YouTube videos, etc. to learn as much as I can before going ahead.

Any thoughts, suggestions, recommendations, etc. would be appreciated.

If I do decide to go with installing new unfinished hardwood (instead of
pre-finished hardwood), I assume that some quick sanding will need to be
done -- but not a lot -- before adding a polyurethane finish. Is that
correct?