I'm in desperate need of design help on a flip.

So, my partner and I bought an abandoned, undervalued, underestimated property in Marfa TX and with no experience, contractor or designer, created a successful boutique hotel, applying an entirely new Airbnb only model.

The limit on one STR permit "per building or property" might be designed to prevent people from buying a 4-plex, for example, and using all the units at STRs.  

For the lower rental unit, I'm interested in a 1031 exchange property in a designated opportunity zone (California's: http://dof.ca.gov/Forecasting/Demographics/opportunity_zones/), which provides for improved basis with cap gains payable on earnings from Opportunity Zone investment after 10 years?

One of my main questions pertains to real estate rentals and I believe that the answer would help me in designing my investment strategy. 

Conventional systems will typically cost less than $20,000, but if an Advantec or other specially designed system is needed costs can reach or exceed $30,000".See Cesspools and the Rhode Island Cesspool Act Frequently Asked Questions and The RI Cesspool Act Goes into Effect 1/1/16: What Buyers & Sellers Need to Know (from which the quote above was taken).You will want to check with your mortgage broker, however, with whether the bank will have a problem with a repair credit that large.

No, it is not an easy fix but why force residents to deal with a bad design in perpetuity that can be remedied within a matter of days and dollars.

It’s admirable to homeschool the kids and stay at home with them but If you are only going to have one employed adult they need to increase the household income dramatically especially for where you live .

It has to be designed FOR rental collection. 

A designation course with BOMA or IREM is several thousands of dollars.