I wouldn't try to pump the floor up any tighter than the main tubes. If you're not going to run anything very technical, it might be worth it to run the floor a little soft. Though the boat will track slower and bail slower. Also I wouldn't rely on the relief valve to signal when the floor was at maximum pressure. I've seen too many blown I beams to depend totally on them. And I've ran one boat that once the relief valve went off, it didn't stop until the floor was flat. Very annoying.
I don't have much experience with how much weight floors can tolerate. I'd recommend trying not to have so much weight that the floor is submerged. If its a laced in floor, make sure the lacing and grommets are in good condition. And be careful of overloading entire the boat, not just the floor. Just because it floats, doesn't mean that it is maneuverable. Hope this helps and good luck with your new boat.