I use this term "business" loosely because most people become "owners of a new JOB" and not a business depending on how you operate it.

Depends upon what you negotiate in your leaseI believe what you are looking to do is called a lease with option to purchase It seems people call it lease option or LO

It depends on your goals, investment criteria, the type of properties, and the Market you are investing in.For instance I am a Buy and Hold investor.  

Depending on your lease agreement, I can see the painting and trim (fill in the trim, then paint it while painting the other stuff) as wear and tear.The garage door, screen door, and floor could all be considered chargeable (again, what does the lease say?)

Depends.

Its a great place for cash flow and depending on your investment strategy there is a very wide range of types of investments.I have been working on the investment side of real estate for several years now and know the city very well when it comes to buy and holds.I own a few myself and have and have wholesaled and worked with a ton of buy and hold investors.You need to be careful of what you are really buy in SA though as what you are experiencing in Austin is happening here as well but mainly on in low-end properties.

If she can't wait that longAustin's solution for seller financing is great but I can tell that neither you nor your friend have much experience in real estate so that may be tricky for you guys to negotiate.Another option is to look for a deal together and you buy the deal and sell her a note for x% financing or partner up on a deal 50/50 if you have the funds.It really depends on your friend's objectives.

It all depends. 

Depending on your area, renting short-term and long-term can be very profitable as the TDYers have lodging allowances that are based on the average daily rate for a hotel, usually $2800-$4000 per month.

It really depends on you're comfortable with and your goals.