Lots of potential sources: other investors, family / friends, personal loans (I've used SoFi & Discover in the past, they loan in the $35-50k range depending on your credit), 401k loan, margin account against stocks you own...Just make sure to factor in those payments in the overall numbers.

The decision on where to invest comes down to a lot of factors including your budget and investment criteria, so it's hard to recommend specific areas.

I understand the factors driving it are different that the last Phoenix bubble, but are these prices sustainable over the long haul? 

. $12k, plus an annual bonus that averages to roughly $1k/month (if that can be factored in)Current monthly debts (including mortgage, property tax, insurance, car, child support): approx. $3.5kDebt-to-income concerns:Time for some napkin math for a concern that makes me worry whether this goal is actually possible...Assuming all goes as planned, I worry about eventually hitting a wall where I'm unable to qualify for new mortgages at a certain point due to how the investment properties' mortgages will affect my debt-to-income ratio. 

Personally, I factor 10% mgmt fee, 10% maintenance in my quick numbers.  

What factors am I not thinking of that I should be?

The pandemic, and other factors, have introduced many travelers to the STR concept.

You see, contractors have a precise mathematical formula on how they charge, and if you think a contractor’s fee is based on their level of expertise, the scope of the job, cost of materials, and or other factors that would make sense, well then, you’d be totally wrong on any one of those instances.Contractors have their method of pricing, and it’s all about you!

I'm considering turning over the portfolio to a property management firm, but when factoring the commonly used 10% of rental rate they charge, I may be better off hiring a property manager (perhaps on a part time basis at first, if not full time).

Rent ranges as follows (depending on numerous factors):1 bed $525-$7952 bed $725-$10953 bed $875-$13504 bed $975-$1500Let me know if you want to talk further.