Plumbing: Can the drain go down into the floor after the p-trap inside the vanity, or must it go in a wall?
I have plumbed them both ways many homes have the plumbing hidden in the walls but sometimes it is easier to go through the floor so whatever is best for your layout is fine, the only negative of going through the floor is you loose a little storage but this is not much a sacrifice compared to the ease of not having to open the wall and with a small sink it can be much easier to go to the side and down compared to back through the wall and then down.