Update with double paned ones.

The windows are in visually poor condition and allow moisture between the panes. 

Aside from a few minor problems that I can fix easily for less than $100 there were a few problems that I consider to be major issues. 1 The TPR discharge pipe on water heater is PVC and drains directly into the drip pan.2 The electric panel is missing the deadfront cover and one breaker in the electric panel has more than one wire connected.3 A horizontal sliding window has been installed as a vertical single hung window in the bathroom.What do you think I should do?

If I were dead-set on that property, or at least that price range & putting 20% down, then I'd be looking to take no more out of the San Marcos property than is absolutely necessary to keep the down payment from putting a serious strain on my overall financial picture.

IF I invest it would be in a cool market where the profit margion is larger and where I can still make a profit without putting to much strain on my renters.  

Defiantly causing a strain financially.

I figured double pane windows, R-30 attic, Foil board and 30-year singles. 

A buddy walking with a cell phone is not going to know if roof is good, electric panel is ancient, if the foundation is sinking, you may need to go there when you do not have the tools in play.

You could also look at the unit itself and see if it is dual pane windows, etc.

I need a window pane replaced, some some alarms installed, and some stove exhaust fans replaced.