I am buying a new house.
The main level and stairs are hardwood. Looks like the type that was
sanded and finished after installation.

At the top of the stairs is hardwood, but the bedrooms are carpet.

I want to remove the carpet and replace with hardwood.

I have a few options.
Remove the existing floor up to the top of the stairs, and lay down all
new floor on the stair landing and the rooms.
Then I can put pre-finished floor without worrying too much about matching.

Or I can put down unfinished and then refinish the entire upper floor.
Not sure about this one since it will be DIY.