From my research, I didn't think there was any magical rent formula but I was hoping there were some generally accepted guidelines that would put me in the range. 

In looking for a manger I see that there is a wide range of maximum repair value that the management can authorize without my authorization.

It is going to be tough for you to find a high LTV conventional loan through a bank or credit union with a property in that price range.

I think I could 1031 each of the duplexes into a newer 2000s later build SFH in the 185-200k range and mitigate a lot of the vacancy/capex issues I’ve been having w the older duplex units.

My listed rents are in the average range for the market they are in. 

Not for seniors who are not self-sufficient and require a nursing home.Thanks for any feedback.If you are interested, I can put you in touch with a company that organizes and finds appropriate types of properties for this need.

Currently a Junior College student , wanted to buy my first investment property either my senior year of college using a business credit or possibly getting some type of Loan for the property, can anyone lead me in right direction was looking for maybe one in the 60-80k range with possibly section renting it from me as passive income.

The pre-approval will last a year so the sooner you do it, the sooner you will know what price range to look at.

I'm targeting NPN notes on houses around the 50-80k FMV range.

In our case, we made the effort because a) we're on our 7th property, b) we have sufficient reserves to weather ups and downs with the property c) we have an attorney we've previously worked with and trust to help us with the resident ejectment, d) the purchase price was low enough to give us sufficient room for error, e) we have contractors with whom we've worked who we believe can timely renovate the property and f) we were prepared to get it wrong and either lose money on this or sell the property at break-even, a small profit or a small loss.