The IRS doesn't have a lot of hard rules about the type of loans (or source of loans) with a 1031 exchange. 

Something I’ve been thinking about is the benefits of loan pay down.

We renovated property doing all the work ourselves so I'm not sure if we can factor in our labor into the money we put into the property, not just materials?

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It ended up being a great deal as the sellers divorced and needed money and accepted a small portion of the loan as payment in full.

30 yr fixed Vacation/2nd home loan with 10% down.

For example, say the investor is requesting funds for a rehab draw and they utilized a GAP loan. 

Yes, nonrecourse loans can be paid down on an accelerated schedule.

You might try and look locally for portfolio loan or DSCR loan.

I'm currently a buy and hold investor (utilizing various househacks), but I'm hoping to get into the STR space end of this year/early next year.In terms of your financing options, here are some things that come to mind (albeit may or may not apply to your situation):- Utilize second-home loan option (10% downpayment) if the property qualifies- Utilize a small local bank to see what loan options they may offer (perhaps some may have experience lending on STR?