I only freedive to shoot fish, and learned this activity from some of the best; very experienced and knowledgeable divers that can dive well below 100'. You should practice alot in the pool first as well as read multiple books on the subject. Look up apnea on the internet...... Also, BlueWater Hunting and Freediving by Terry Maas is an excellent read.
The best freediving months in Texas are april-jun, the thermocline is much higher as well as the fish. Late July to Sep, you will have to dive well below 60' just to get a look, and no room for error. Rig diving is the way to go, you can ambush fish around the rigs, also generally no sharks (generally).
Freediving has got to be one of the most challenging and rewarding experiences life has to offer. I hate to say, but compared to tank divers (spearfishermen) it is 1,000 times better if you can train your body to do it.
Any questions shoot me a pm.....