Properties equipped with the latest technologies and sustainable features often command higher prices and rents, enjoy lower vacancy rates, and have reduced operating costs.

Does anyone know how true this is and if mortgage rates will keep going up? 

If so you definitely  need one.If you or most all of your competition doesn't have one then it's not necessary but it may help set you apart from the competition if you need to increase your occupancy or nightly rate.

The only con is the higher interest rate. 

The issue here is in order to increase rents at reasonable rates to cashflow well you need to not just do cosmetic changes they require you to do extensive plumbing and electrical to be able to increase the rents. 

There's a lot of moving parts here but it sounds to me that you owe them at most the original $150k + a conservative 8-10% interest per year (well above market rate).

I thought about doing cash out refi, but my current rate is 3.5%. 

I recently started to have an interest in houses in Philadelphia and I noticed that there are some cheap houses there with squatters. 

And I could have lower income in that window after I semi-retire, before my mortgages are paid off to take advantage of a lower marginal tax rate

- if everything is too cheap- if they mention more about their acquisition rather than how to maintain your property- if they only have two people in the office- they don't know how to manage property.- no bookkeeping.