So borrowers need to qualify for the full draw amount with current investment property interest rates of near 12-13%. 

Yes, it can feel like "wasted" money on months where rent is auto-paid and there is no maintenance to be done, but when you get a bad tenant or two or when deferred maintenance finally catches up to you, they certainly earn their keep.At your scale, you might be able to get a bulk discount with a good PM, especially if you can show how well your current systems are working and how they'd be needed less than usual.

I’ve thought about selling our current house, using that equity to pay for a single family fixer upper that we’d work on for around a year, and do it again.

I currently own & operate two STR‘S in SoCal USA, both fee-simple, no leasehold, so I’m new to this concept. 

Do I have to refinance with current lender or they will deny any refinancing deal with me?

Some say there are still opportunities in Columbus since it's growing, but I'm unsure if investing with the hope of future appreciation is a good idea when current cash flow is very weak.

I'd love to hear about your current or upcoming projects and discuss how we might be able to work together.

This starts early on with preventing what could potentially go wrong by attracting an awesome tenant and looking at what vulnerabilites currently exist in your property.  

Conversely, are there any areas I should avoid due to high crime rates, low rental demand, or other issues?

I am currently reading Brandon Turner’s book “ investing in real estate with no and low money down”.