A ductless mini-split is a heat pump with an indoor head on the wall and an outdoor condenser outside. Before you commit, the questions that matter are about the spots the unit will occupy and the work it will need around them. Get written answers before the order goes in.
For the typical service life of a heat pump and how to plan around it, see the heat pump page on this site.
The indoor head
Ask where the indoor head will sit and what clearance the installer needs around it. Ask whether the air will reach the places you use most, and whether a bed or a couch would sit in the path of the airflow. Ask how the condensate drain runs from the head, and whether the wall has a clean route for the line set and drain that does not require cutting into a structure you cannot reach later.
The outdoor condenser
Choose the outdoor spot with the installer. It needs a solid pad or mount, room for airflow, and a route for the line set that stays protected. Ask how far the line set must run and whether the installer accounts for that length in the setup. Ask about noise as well: where the condenser will sit relative to bedroom windows and neighboring walls.
The electrical path
Ask which circuit the unit will use and whether the panel has room for it. A written answer is better than a guess. If the panel is full or hard to reach, the panel plan comes first. The electrical panel page on this site covers typical service life and when to plan a panel job. Electrical work itself belongs to a licensed electrician in most places, and the installer should say who handles it.
The paperwork and the service plan
Ask who pulls any permit the job needs. Ask what the installer includes: the line set, the mounting, the disconnect, the drain, and the start-up check. Ask how the system is set up and recorded at the end, and whether you receive a copy. Ask what the written terms expect from you as the owner, including filter cleaning and any scheduled service. Ask how service is reached if the unit stops heating or cooling, and who answers the phone.
Write it down before the order
Put the indoor spot, the outdoor spot, the circuit, the permit owner, the included parts, and the owner tasks on one page. Sign off only when every line has an answer. A clear page now saves a later conversation about who was supposed to do what.