Yes to urethane single stage because there is also acrylic. I haven't sprayed much of it because by the time I started we were mostly using urethane. I've been told though that it doesn't hold up as well in both durability and shine.
Sealer is like a low build primer that you don't have to sand before tip coating. You let it flash for about 15 minutes and can spray over it. You will still have to scuff it up if you let it sit too long though. I really don't see the need for a high build primer, unless you want to fill in every little scratch and sand it down super smooth.
After it's cured, normal foot traffic shouldn't bother it. It is still paint though, so dragging hard/heavy/sharp things across it can still damage it. That's going to be true for anything though, unless you want to make one out of stainless. Even that can still get worn. Nothing is indestructible.
