The HELOC shouldn't affect your credit until you use it, and thus the juice starts.

The biggest factors that really juice overall returns here are rent increases and appreciation.

Conventional products are always going to revert to market rates and they won't use your juiced up returns renting by the room. 

@Scott Bell I can be a resource in Greensboro.

I did have 3 AC units go belly up in June. $10,000.

It normally covers the basics or enough to protect their you know what if it goes belly up. 

The market is being juiced right now because rates on houses are at all time lows near 3%, what happens if rates go up 1% to 4%? 

Personally, I'm focusing on STRs right now but it has nothing to do with what is "safe" but everything to do with a willingness to run a very active business to increase our income and juice our returns vs a less passive approach of LTRs where our return is much lower.

I think the juice is worth the squeeze.

Also, look into the possibility of renting out rooms to see if that will juice your returns or not.