The investment city determines rent growth rate, appreciation, and income longevity.What determines rent growth?

It's going to offer Strong economic growth, Appreciation (especially in DFW), Tax advantages (no state income tax), and a Growing population, including infrastructure and amenities. 

This property gives me significant income, so losing it would be an extreme loss.

It varies by program.To learn more about DSCR programs: DSCR loans won't use your income to underwrite the loan.

If my target would be low income residents, are there any grants, tax credits, or funds available to help me with the conversion? 

Are you looking for steady, low-risk passive income now, or are you comfortable taking on more leverage to scale faster?

If the way to increase the selling value of a MFH is to increase NOI by increasing income or decreasing expenses; why are the majority of sellers putting their properties on the market with under market rent?  

If you have some capital, income, and decent credit, buy a 4-5 bedroom house and rent bedrooms. 

Everything I'm finding says 27.5 years due to it being rental income but others say 5 years because it's an RV.

Im a huge fan of themI think both - they will bridge the gap with middle-income renters and also appeal to the higher-income bracket.