I'm unsure if you would be able to combine both loans given that the HELOC is tied to a different property than the one you got traditional financing on.A work around is if you are able to purchase the new property with the HELOC at a significant enough discount, bring the property value up via renovations or additions, then refinance the property, pulling out enough money to repay the HELOC. 

These will be LTRs and I will most definitely be playing the long game with these.In addition, as rates go down in the future (hopefully) I plan to refinance as most of us do.

That way, you can get your foot in the door, start building equity, and stay at home a bit longer to save more money.You could also consider the BRRRR method where you buy a fixer-upper, rehab it to add value, rent it out, and then refinance to pull your cash back out.

You will owe monthly payments until you fix the property up, rent it out, and refinance to a more traditional 30 year fixed rate product. 

There are a couple of companies out there that will let you do a cash out refinance with no income!

I remember being excited to refinance at 5%.  9% was good rate and plenty of loans were 12% or more.

Assuming rents go up 3% a year and interest rates are hovering 5% and i refinance from 8% to 5%.

Buy and renovate the property and in 6 months do a simple cash out refinance and pull out some cash and start the REI process all over again.I am North of you up in Pinellas County West of Tampa and there are also some great places up here that might save you some cash. 

And equally for the buyer, if you want to renovate and refinance or cash out, wouldn't you have to pay off the entire mortgage at that point and the bank would know it was always the buyer paying off and not the seller?

Quote from @Robby Sanchez: can you refinance at the end of an interest only loan into another interest only loan?