First off, March is the begining of the 1st summer we have here (1st, 2nd, & Hades), so don't worry about cold weather. Just make sure you pack a light jacket for at night. Jason's Deli would be the best place to have cater, and they are on the web.
www.jasonsdeli.comAs for fun, try going to a place like SpeedZone (racing), or take a trip to the WestEnd (dinner & shopping). If your guys can handle the odd side of life, Deep Elum would also be good (clubs, shopping & street vendors/artist). Dallas also has quite a few good local bands. The Bronco Bowl is another good one (big club/bowling alley/ arcade...)
Ellen in TX