Expect a site visit with a heat loss calculation, a look at where outdoor units can sit with room for snow and airflow, and a plan for line sets and condensate drains. The town's Master Plan says lakeside neighborhoods around the Monponsett Ponds often have small lots, so if you live there, ask to see exactly where the outdoor unit will go.
Permits run through the Building Department: a wiring permit for new circuits, plus building or mechanical sign-offs as the job requires. Inspections have to be requested at least a day ahead, so build that into the schedule. If the old oil burner or tank is coming out, ask whether the fire department needs to be involved.
Installation typically takes one to several days depending on the number of indoor units, followed by start-up, a walkthrough of the controls, and the rebate forms.