Our plan is to hold this medium-term rental property to build equity and develop a larger portfolio soon.

This could help you build confidence and add to your capital without the pressure of a larger, more complex project.You’re right that the Nashville/Central TN market has been hot, and while it’s cooling, rates are favorable.

Make it a larger gift.

This is a ground up development with shallow and larger bay flex space. 

For me when I'm estimating rental income I start by looking at the area for active listings <40 days old with similar characteristics to the home you're looking at purchasing (trying to find same bed/bath count, and same amenities like in CO homes with a fenced yard do very well because everyone has a dog).

My brother lives in this subdivision and rents a 2 bed 1 bath for $500 and I have a home on the same street, larger, that I rent for $780 so I know what the rents are.

The point of the government requiring some larger investments to only take "accredited investors" is the paperwork you agree to specifically says you could lose all of your money.

Without an exact numbers breakdown of each option (which should obviously be my next step), I think my ideal situation would be to sell the SF and roll the equity into this, leaving me with a modest holding cost that I can absorb with my stable W2, and keeping the HELOC for any larger ticket items I need during rehab.

How they've been in the property for 2 months storing their dogs there with no rehab movement, while putting sweat equity into it, but haven't addressed the foundation or any rehab issues yet.

Tenants expect them and it is better to increase a small amount every year then a larger amount after several years.We typically know what market rent is from the turnovers and keeping a long-term tenant slightly below market seems to be the sweet spot.