I'm hoping to see her in Houston too! She hasn't been here since the Blond Ambition Tour hit The Summit in 1990! As for your questions:
It's too early for setlists to have been released, but as August 23 approaches, go to www.drownedmadonna.com or www.madonnalicious.com for any rumors. After opening night, it's fair game...expect to see the setlist at any Madonna fan site. During her Hard Candy Promo Tour, the setlist was: "Candy Shop", "Miles Away", "4 Minutes", "Hung Up" (rock version), "Give It 2 Me" and "Music" (fedde le grand remix). It's a good indication that these songs will end up on the Sticky & Sweet Tour. Also rehearsed for the promo tour was "Borderline", so that's also a possibility.
Ticketmaster.com should have the layout for Minute Maid Park sometime soon. Right now all they show are Astros layouts. I googled "Minute Maid Park Concert" once and came up with a concert layout, but it was at a scalper site so I'm not 100% sure of the accuracy. It showed the stage at the far end of the field, opposite home plate. There were 16 small sections in two rows directly in front of the stage, and then there was the rest of the arena. The front half of the field was empty. Keep an eye on Ticketmaster.com though as May 31 gets closer!
I'm not sure if you've seen a Madonna show live before, but it's truly an incredible experience! Good luck with tickets!