If you have the time and experience, hiring your own subs (like plumbers, electricians, painters) can save you some money, but you'll need to manage the project yourself.

I will cash buy as I don’t really like their financing and don’t want to deal with currency fluctuations causing my payment to change month to month. 

My STRs and MTRs are cash flow negative.  

The fact is I don't have million dollars in cash sitting in my bank account.

The cash out refinance gave us roughly 60k.

Get rid of debt, build a budget, and save.

Maximum cash flow is absolutely vital.

as a break between living spaces.I'm not a builder but I imagine builders enjoyed a little savings by not having to budget for all the additional interior walls, but maybe that money had to go into costs anyway.Open floor plans are nice, but a bit too open for me.

Do you have access to the paid version of airdna to find comparable properties that are cash flowing at 500-650 a night? 

I presume you are trying to "add value" in terms of increasing cash flow, not in terms of increasing the value of the home (for you to later cash out refinance)?