Understand the fees involved and calculate the total cost for an entire year of management so you can compare the different managers.

So if there is a fire due to natural cause, HOA insurance will cover the cost of exterior repair like painting the exterior walls.

Total cost of land and size?

The only approach I’ve found effective is offering a deposit alternative, which lowers upfront costs for tenants without devaluing your property.

Architecture did a design and well respected contractor estimated the buildout of 4 plex would be an additional ~800k for total project cost of ~1M. it would be ~1.2M for the 7 plex.  

The triplex is much more popular with traveling work crews for specialists in the trades and insurance relocations, so if we were to do it again, I would probably worry less about making each room it's own rentable space and save a little bit of those costs. 

It will likely cost you several thousand or more to rehab the home upon turnover.

Can anyone provide insight on the average cost of insurance for Airbnbs with pools in the Boston area?

The best projects I've seen from my desk are folks who are doing hyper-targeted, well-researched deals that are generally in higher cost of living (there are exceptions) areas. 

After a bit of back-and-forth on the repair costs, I negotiated it down to $69,000, convincing them the extent of repairs was higher than they initially estimated.