I am just looking for insight from local MA realtors, attorneys or landlords regarding what my typical monthly expenses (if any) will likely be (I don’t mean one-off expenses like roof repairs). 

My experience indicates that solid due diligence upfront on the economics is the critical factor, the tax aspects often take care of themselves with only modest planning.

That's actually a great aspect of real estate, if things don't go as planned, wait it out!

Actually, a friend once mentioned a unit in Eugene that had to be re-leased after a nasty storm tore off part of the roof.. it’s gritty, hands-on stuff like that which rounds out your perspective.At the end of the day, you don’t need a flawless blueprint to get started.

It had some deferred maintenance and I put a new roof on and fixed a few things.

Also the value (in this case) is determined by the NOI, so assuming it will be worth 2x, is assuming your NOI is thru the roof (which is can be, but it's not likely in the first 5 years).

To them a 5 year old roof is in good shape for the near future the same as a 18 year old roof.

During your initial walkthrough, inspect the property for any major issues such as structural damage, roofing problems, plumbing, and electrical concerns, while documenting all cosmetic and functional issues with detailed photos and notes.Once you confirm the property’s potential, finalize your ARV and calculate the repair costs using either a reliable estimator or insights from contractors.

These include accidents (I recently had 2 units destroyed by fire), natural disasters (I have had two units each hit by 2 hurricanes), property management turn over (they sell or stop being as good, I have experienced both), or turn over of team (I am turning over at handyman and I suspect plumber), or just wear n tear of property (slab leak in poor location, sewer pipes rotted out (one unit this month), roof, foundation issue, etc.).  

For example, on a recent project, Draw #1 covered the roof, demo, and trash-out.