Generally speaking yes, using a HELOC as a downpayment on a commercial should not be an issue especially since it sounds like you have sufficient income to support the debt payments 

Here is an empty building, come sleep here.

Trust me I get it I'll be 28 this year as well and wouldn't prefer doing it but it's allowed us to scale much more quickly than we would have been able to in the last few years.You can just PM me the address and that should be sufficient.

Both STRs do have an uninterrupted history, but not a complete year yet, 11 months on 1 and 6 for the second.  75% may be an option.  80% I'm positive will provide the funds I'm seeking while maintaining sufficient reserves.  75% isn't out of the question, but I don't want to decrease liquidity too much.

If you really really wanted one, I'm sure I or anyone else could drum up some nonsense, but as of now the market isn't sufficiently large, doctors more often want the big shiny single family house in the prestigious neighborhood, for whatever reason.I've never been a doctor, but here's something I've noticed.

Your basic insurance policy with $300,000 in liability coverage should be sufficient in 99.999% of all lawsuits.5.

Here is the summary:  Any place that is designated as a sleeping area needs to have 2 means to escape. 

It was a lot of lost sleep, heated exchanges and multiple trips to JP court.

I would carry sufficient liability umbrella to cover your assets regardless of a specific occurrence.

That surplus should flow downhill.I would certainly not notify the HELOC lien holder of this situation as that could wake a sleeping creditor and create a new foreclosure action with you as the defendant.