After a load calculation and a look at your ducts, attic, and panel, the installer should give you a written plan that covers the heat pump, the electrical work, and what happens to the oil system. If the oil burner and tank come out, they're part of the job's fire department inspection, which the installing contractor must request within 7 days of finishing.
Expect the permit card to be issued before any equipment is set, since Bridgewater can triple the permit fee for work started without one. Mass Save also reserves the right to inspect a project before paying a rebate, and some jobs are picked at random, so keep the invoice, permits, and photos together.
If the house sits low near the Taunton River or a brook, the outdoor unit belongs on a raised stand or wall bracket, set where meltwater and heavy rain drain away from it rather than pooling underneath.