I think the absolute necessary things are new flooring and paint inside and out, new light fixtures, some new interior doors (or just paint the old ones), new interior baseboard trim, 3 new exterior doors (change 2 sliders to French doors), siding installed on side of the house at least and maybe the back too, change out main front entrance door, new oven, rebuild the deck off master bedroom, and minor landscaping.

I like what Mike said and he is right.I offer with a letter of intent (LOI) that outlines 3 scenarios and prices which would work for me. 

(city water main broke and flooded basement) insurance work was approx. $25,000.

So many investors don’t know the the benefits of that.Asset protection is the main reason for having LLCs as mentioned by @Saberian Younger  The answer to your question will become obvious when you do your taxes.

However, it can legally be used as a bedroom/extra room for the main house.

I have seen on this website answers both ways regarding this (the site administrator saying leave it in Sch A, and his colleague (also a enrolled agent) advising that it can be written off in Sch E, but that there are certain restrictions mainly -- you must have passive activity gains where the deductions are covered (no passive activity loss carry over allowed.

Are you investing mainly for cash flow, appreciation, or long term equity build?

Main issue: if you add an ADU the property becomes a 2 unit bldg., which means it’s under rent control for both units.

I can't afford the Boston area, so I've invested in property in Maine. 

The main aspects of real estate that I am interested in would be owning rentals, and working as a RE agent.