Cash purchase then refinance?

[Thomas B.]

I'm trying to navigate my way around the best option to finance my 1st income property. 

I'm looking to invest in small 2/1 or 3/1 single family houses in the lower income neighborhoods of the city where I live. They typical range from 40-75K. I can use my TSP (Fed employee 401K) to loan up to $50,000 at 0.75% interest with a 5 year term.

I plan to rent to Section 8 since the HUD Fair Market Rent for our county is considerably higher than many of comparable units in the area are rented for. There is a lengthy list of applicants and the rent partially guaranteed by Big Brother too.

In the BRRR strategy, at what point would I need to refinance? With a 5 year term, the $849.32 payments are unsustainable for very long. Is there a time period I have to wait after the initial closing before refinancing?

Would there be any advantage to doing this over using my TSP loan for the down payment on a conventional loan?