Non-QM I can do things like bank statement, self-employed, ITIN, Jumbo, blah blah blah.

It was a conventional bank loan.

If the HELOC rate gets out of hand, then go to the bank at that time.

Easy to use yourself too HELOC works (there may be some places that do a HELOCs on rental properties)I personally have used a 401k Loan on a few occasions - You're essentially borrowing money from your 401k and paying yourself back (interest goes back into your 401k as opposed to a bank) and if you don't pay your 401k back the loan would simply become a withdraw (maybe some tax penalties, but you could probably finagle a workaround).

in what I just laid out, you'd make monthly payments to the seller just like you would to a bank for 5 years, and then the remaining principal balance of the loan would be due, at which time presumably you would refinance the house into a commercial mortgage and use the proceeds to pay off the seller. 

You typically will see small banks/credit unions probably wouldn't be able to out-of-state, but otherwise any mid-size company or larger should be able to.

.✅ Seller Financing – Skip the Banks & Get Creative!

But each LLC should have it's own bank account. 

There's actually a good chance your overall "cash out" with the HELOC will be higher (most banks will go up to 90% vs 80% is generally the highest a cash-out will do) albeit at a higher interest rate, but you can protect the original mortgage rate if its very low (2020/2021 rates).Also consider the flexibility of only pulling on the HELOC when you need it thereby keeping expenses down.

Then refi with my bank for 30 years.