The other "economical" areas are going to be more management heavy (think cheaper houses that are expensive in the long run) and the A/A+ neighborhoods will be very difficult to get cash flow (think Elmwood Village or Hertel Ave duplexes that are $350-400K but gross $3600/mo on the top end). 

Combine this with poor ADU valuations (especially in single family zoned areas) result in hands off ADU additions costing significantly more than the value they add.  

I have looked up building companies in the area, joined Facebook groups, posted on Linked In, searching the MLS, and have a networking event coming up. 

Or a separate area of house with private entrance/exit?

I would like to know which are the best zipcodes to invest in and how is the rental market ion the area.

The property is located in prime location and we would like to keep it as STR since selling right now is not the best strategy in that area, but we believe in that location for appreciation therefor we really want to keep it as STR.

I think so, however the common areas, including exterior, would need to be Lead Free as well.

One other thought too- if you feel like you are having too many deals, maybe then your buy box may be too wide, and and you can narrow in on what area / location / return you truly want. 

I am also from Newburyport if you know the area!

We also do a few other things on move-in day.... we put drop cloth runners down in the traffic areas, loan the tenants the use of moving blankets, furniture sliders, an appliance dolly, and shoe covers.