Are there tenants looking for mobile homes to rent, and what are the going rates?

But to answer your question, House canary is good for rent rates, zillow is a good tool for property data and for seeing what is for rent for how much, sales comps etc. 

What is the interest rate on your student debt? 

This home has been highly operational with high rates of occupancy, bringing in anywhere from $500-$1500 a month in overage beyond our monthly expenses.

A 6%+ annual appreciation rate is decent. 

It's a guaranteed rate of return above and beyond anything you can get in the market or real estate. - The 4% rule is a helpful benchmark but leaves a LOT to be desired in terms of projecting retirement income from a liquid portfolio.

Don't look for lowest rate, look for lowest cost on fees as you will either refinance out of that loan or sell- the prepay will hit you on the back of the head like a cinderblock wall.

maybe they would do a subject to and have you take over their mortgage payments - do they have a good interest rate? 

Are there any ways to use the equity that don't have brutal rates?

Lenders or investors who have short lock up periods but have years of experience feeding their business with new capital would give me more comfort but anyone who is just starting and is promising a rate of return or return of capital in a set period of time would be alarming because they very well could be reliant on fresh capital to make good on that promise and that usually ends poorly.