I'll answer what I can, just based on being local and also from the info I've heard or read from others on the Galveston cruises. Hopefully someone else will pitch in too.
1) No, they didn't move any of the
DCL motor coaches to Houston.

The transportation company that they had been using while the Magic was here was Woodlands Express. I don't know if they showed any video, hopefully someone that has taken them can help you with that.
2) You have to claim your luggage and meet the DCL rep outside of baggage claim. I assume that they will offload it from the motor coach for you and take it to be loaded on board, but again, maybe someone that has done it can say for sure.
3) If you land at 10:14 am, then I would think you'd be down to the cruise terminal by about 12:30 pm-1:00 pm.
4) Seeing as you have a late flight out when you leave, I would take my time getting off the ship and take the very last coach available. I would think the last one leaves about 9:30-10:00 am, so you'll be at IAH by 11:30-12:00 pm. I've been trying to think of something that you could take a taxi and go and do, but there's not much out by the airport.

The airport has quite a lot of shopping and some good restaurants and bars.

This link has a terminal map that you can click on (C and E have the best facilities) to show you what is in each terminal. You have a long time there though.
http://www.ifly.com/george-bush-intercontinental-airport/terminal-map
HTH's