They used reclaimed wood (that I'm sure they just made out of 2x4's and stained, with cool looking brackets). 

Do I need to stain them?

I don't know what @Rosston Smith is thinking but something along the line of a sandstone color or a light beige with white trim would probably look good and the little bit of brown in the paint would hide minor stains for longer.

The granite countertops require much maintenance so the spray should be such that it does not leave any kind of stain on it though the granite being water resistant.

I strongly feel that white trim is preferred these days, as opposed to stained wood.

You will get oil stains here and there over time.

Her plan for the floor is to make it stained concrete although I think commercial plank would look nice.

They usually start out with dark stained wood.

No sagging floors, no water stains on basement walls or floor moldings, no water stains on ceilings or walls, no mold or mildew, updated electrical panel, newer windows, etc.

Those nicotine stains are unreal!