No. Unless you put a veneer on the ends. They call them end skins.
The wall cabinet can be flipped upside down, so you do not need to rehang the door.
The inside actually already has a very nice factory finish.
Yes, I bought one just the other day.
Just one. I bought 10 inch wide pine and stained it with a clear finish, unless you are looking closely you probably would not be able to tell the difference. The ten inch wide pine boards are not quite wide enough for the wall cabinets, so I put a couple of 1/2 inch bumpers on the back of the shelf or you could add some molding that could do the same thing.
Yes all you need