Stubhub or ebay always have tickets, and usually pretty good seats, depending on how much you want to spend. You can always buy tickets on the street.
I thought the stadium tour was pretty cool, so if you're into things like that, it's worth it. The Astrodome tour was better, IMO, but mainly because of the history and the whole growing up in awe of the Dome thing.
As far as Hotels, the Hilton Americas is a very nice hotel that can't maintain occupancy, so it's usually pretty easy to get a great room at a good rate (I heard $88 per night recently). It's a couple of blocks from MMPUS.
Again it depends on what you want to do when you're here.