For the record, there is no sales tax on flight training in Texas. Any aircraft rental or instruction that could conceivably be purchased for proficiency or training is specifically exempt in the Texas state tax code. See the Texas Comptroller of Public Accounts letter
200809501L. This came as a surprise to me when I started training people in my C150, having previously done so in Indiana and Michigan where collection of sales tax is required.
Cessna 150s are great trainers. Make sure you take a look at the SAIB concerning elevator attach point corrosion. Even though you're Part 91 and the SAIB technically is not mandatory under the federal regs, any lawyer can frame you as negligent for failing to comply with it if your aircraft is involved in an accident. Also, as someone who trains people in my own plane, I wouldn't bother with having just an A&P look at my airplane. I have an IA who does it in a reputable shop. That's not to say regular A&Ps are bad by any means, but if you want to mitigate the chances of being framed as a guy who skimped on maintenance, going with the highest certified mechanics to do (or at least certify) the work is your best bet.
That said, the 150s also have serious engine cooling issues in the DFW area from April through September. Consider getting an oil cooling kit installed. In the absence of that, you'll need to develop procedures that ensure students and instructors aren't scorching your cylinder heads beyond their limits. That may mean the airplane remains unused during the hottest parts of the day.
I highly suggest you read Practical Aviation Law by J. Scott Hamilton. He goes over a lot of aviation-specific liability concerns that we almost never touch as topics of conversation on this board.
Finally, go for it. It's fun.