Hi Randy Welcome to permies!
I think that 12.5 acres would be large enough for all you want to do ...EXCEPT... growing Hay . Growing, cutting, baling hay, takes a lot of land and specialized equipment that is not cheap. Possibly if a neighbor is growing hay they might be able to cut and bale for a price... Depending on how much livestock you have .. you may need more than you can grow. Buy it from a neighbor.
Water or the lack of would be my main concern. Wells can go deep and still hit sulfur water . They also are not cheap. A windmill pump for livestock might be something you could do.
Your A-2 heifer (does not have to be a jersey there are others) is an excellent idea , however your bull must also be A-2 if you want / need A-2 milk products.
Your in Texas... it gets hot... I might just leave that pool around for the hot dusty homesteaders to relax in after a hard day ... :) just a thought.
I am a big fan of growing black locust ! Firewood , fence posts the only downsides are the thorns and needing new chainsaw chain because the wood is so hard your chain constantly needs sharpened.
Electricity, solar works well, wind is also a good tool in windy Texas. Battery's are the weak link. If you are 100% self sustained you will need a large battery bank. If you go grid inter tie then you will be dependent on the grid staying active...
Cooling in Texas will be a biggie. I'm sure A/C is king down there. With off grid living A/C is a power sucker... some folks make do with a home built swamp cooler. Others just use a fan...