Yes, if you are looking for existing homes Realtor.com and just filter (muti-family) in the property type.

My guess is when you call the town they’ll tell you getting a 4th legal unit will be tough and require you to install a sprinkler system and therefore the CBA will not make sense.

So we know there must be issue will all these systems but the house fits my family needs and we can turn additional space into an apartment for rental.What option do we have besides walking away ?

For this reason, you need to look at your competition during that week that you are marketing the property.I only use a few filters.

I have since put in new hvac system, changed layout from 1 bed to 2, new roof and full electrical upgrade.

What systems do you need at 100 units? 

I use RentoMeter, as well as our own system to compare with other homes in the area.

People having success with this model are buying within a narrow search criteria (4+ beds, 500+ sqft per tenant, 3+ showers, plenty of parking, no HOA restrictions prohibiting non-related occupants, proximity to major employers etc etc.) and hiring management that specializes in the model and has systems + methodologies in place to account for turnover, roommate politics, common area cleaning, utility costs. 

When I think about rehabbing, financing, property management, and other aspects of the business, it can feel a bit disorganized.I may be getting ahead of myself here by thinking about documentation and systemization, but I'd like to have some kind of mental framework regarding how to think about the different aspects of real estate and how they relate to each other so that I can have a bit more structure in my thinking. 

As you learn and surround yourself with like-minded individuals, you will start to put together some systems, processes, cost analysis, and other marketing research that will help you make informed decisions rather than just "a hope and a prayer".