Your assessment and the student’s goals should help to guide your choices. If someone is using a wheelchair then it is likely they will use a sit ski, if someone uses crutch(es) then they may need outrigger(s). Be aware though that fatigue may influence the decision as will the student’s goal such as just wanting to experience the mountain for a day or wanting to be able to ski/ride with family and friends every winter.
When setting up equipment your goal is to have the student standing/sitting in a comfortable balanced position over a flat ski/board in a stance that allows them the greatest range of movement.