@Bob Bowling Net operating income / purchase price

As far as operable windows go, vinyl sliders are about as cheap as they come.  

@Tyler Divine, are you asking about operational type (e.g., casement vs. hung), material type (e.g., vinyl vs. wood), or ???

If I was the OP, I would get 1 secretary per 3-5 projects, have a small 5-10 page operations manual, that will cover scoping, bid soliciting, contracts, and punchlist. pretty much after your 10th flip, you will get your price points already, so just measuring and scoping is the hard part to learn, everything should trickle down feom there.

Easiest to setup in the state that you are going to operate in.

They are sometimes taken advantage of by shady operators.

The tenants cover most expenses so there is minimal room to create operating efficiency, and the likelihood of materially pushing rents is probably low. 

Some operations were offering free housing, so they could bill for the testing.  

What areas of Indiana are you going to operate in?

Point #3 as mentioned is less passive then #1 & #2 it will come down to your confidence in your operators ability to execute.If you decide to take on #4 this will take quite a bit of your time.