How do you adjust the columns when you use a foundation?

as long as the columns are sitting on top of a foundation and not the floor they should adjust. If not just delete them and place them again. Idk, for me personally, if the columns are not also sitting on a foundation (when on the first floor) they will not reach. So like if I want a deck/patio I can't just use tile, i have to add an actual floor (like you'd find in a room) and just have no walls.

As for the stairs, yes they auto adjust to the height.