First: consider the building envelope and upgrading the insulation and air sealing in the house if that has not been done. The Cape Light Compact’s energy assessment program is the place to start. You can have an assessment every year (you pay into the fund through your gas bill and electric bill). Here is the link to sign up: https://www.
Second: Be picky about the manufacturer and the energy rating of the equipment. We have seen far too many installations of mini-splits as well as regular heating equipment that are not energy efficient, miss out on the rebates and end up costing the homeowner more for operation.
Third: It is also very important to be there with the installer to tell them how you use the space so they keep that in mind as they make their assumptions about where to install the heads. Some installers will propose a head in each bedroom, but in many cases, if there is one in the hallway, depending upon how people use the rooms (close doors, etc) it is enough.
We are happy to share the companies we know do good work in the area. We offer a service to members to look over the proposals you get to help you make an apples to apples comparison as they can vary so much by installer.