My dilemma is I feel there is a lot of opportunity with this particular home and the lot itself as an ADU can be added (as either long term rental or STR) however am concerned with the potential risks (both cost and tenant facing) with it being a pre 78 home. 

In most cases, these would have to be purchased as separate policies, or be added to your current policy upon request w/ additional premium. 

In some of the markets like Waltham and Everett that could be adding bedrooms in the basement or attic or utilizing dead space but you need to get a little creative.

Railing can also be added to the steps as an alternative to a ramp. 

My question is, if my final loan will be for 80% max but we found a couple other things that could be added easily- namely, adding a bedroom to the 1bed/1bath side and reinstalling central air (and heat?

I do believe that provisions can be added into a contract for a loan that allows them to do this you'll want to check your paperwork to see if what you signed also gave them permission moving forward.

Otherwise, the fees behind it will just be added weight to your yearly costs, and it may not give you the full benefit you are hoping for. 

As a group we will be adding major value through infill, park improvements, billing back water/sewer & small rent increases.What was the outcome?

I have a truss system and therefore there are no LVL's in place to drill into, but blocking can be added across the trusses.

They have an email thread between the seller's lawyer, my agent + my lawyer (that he forwarded to me once before)Question: Can I ask to be added to this thread?