Wow! What a great price! I recently was trying for 3 package deal here in Arlington (2 quadplexes and a triplex) but the owner was insisting on $249k each for the quads and $199k for the triplex. He also wanted cash only, no showings, had no maintenance records, and no rent rolls.
The numbers do look pretty good. I would definitely factor in the roof though at 15 years old - it is pretty close to the end of it's life cycle. With all of the major storms that hit the area last year - what are the chances the current owners insurance will pay for a new roof before the sale? If not, maybe negotiate a portion of the roof replacement into your offer?
If the 2 HVAC units and a water heater will need replacing soon - have that in your budget and replace them as soon as you take ownership. I'm sure you know how Murphy's Law works in Texas. The first time temperatures hit 100°+ both units will go out on a Saturday evening. lol
Good luck!