Hmmm it has been a while now since I served (in Canada not Houston). I recommend (2) two-pant suits sets for sure. Most missionaries in my mission would wear out their pants long before their suit coat. Hence having twice as many pants as suit jackets being a good idea. I'm sure any of the three listed suit places would work out. I think I got mine at Mr. Mac. When I was at the MTC they (the BYU
bookstore presumably) was making a killing by convincing the missionaries that the messenger style bags (for carrying your scriptures and stuff around while you were out and about) they sold there were only ones approved for missionaries....not true at all so don't fall for anything like that. I suggest searching around the interwebs to find a Houston missionary reunion type site and asking around on there for mission specific suggestions for clothing and other recommendations.
Not sure what is on the missionary clothers list these days but generally I would say: (2) 2-pant suits, (I would avoid wool suits in Texas). 2 pairs of dress shoes but try to find ones that are comfortable for walking (you are likely to wear at least one if not both pairs out) + a good pair of general purpose sports shoes that you could play/exercise in and wear while doing service prjoects. Probably mostly short sleeved white shirts for Texas (maybe one of two long sleeve for certain occasions). And probably something like 10 pairs of garments and socks (you may need to buy replacements during your mission at some point). I made it through my mission pretty much with my original garments but I knew some other missionaries would get pretty worn out and need to be replaced or stop fitting comfortably due to weight changes(we generally had a lot of dinner appointments and many guys left the mission 20 lbs heavier than when they arrived).