A great agent is your brain trust.

On the other hand, a cash-out refinance of your current duplex is another avenue to explore, albeit with considerations such as the risk of losing your low 3.5% interest rate and increasing your loan amount and monthly payment, thereby reducing your current positive cash flow.

I'm new to this but I'm studying it all everyday and I'm looking for a mentor, somebody I can trust.

Be sure to lay out the terms clearly in writing, get signatures on everything, and hold payment until the final walk-through and key handover.

This house as is is worth about $340,000 I would be purchasing it from him for about $320,000 with a $30,000 down payment. 

For background info:*I have a trust that owns a holdings LLC, and that holdings LLC owns my operating LLC.

I have $18,000 saved to use for a down payment and closing costs.

Our mortgage payments started at $2300, but due to increasing property taxes and insurance, they have alarmingly risen to just under $3300.

Even our short-term rentals had a rental agreement with policies for payment, penalties, rules, etc.Here's something from AirBnB regarding rental agreements: https://www.airbnb.com/help/article/465 

On my end, I set my payment schedules, how it will be delivered, level of work I expect, etc.