Constitution is used for calculating hit points and spell concentration saves. Wisdom and Charisma are used for morale checks. Strength, intelligence and dexterity are optional and are only included here for completeness.
Hit Points: Damage Tracking
Hit Dice / Level
Hit Dice and Player Class are only needed if you want to allow for random hit point rolls. If Player Class is set, random rolls with use that, otherwise size, for hit die type.
Difficulty Check: Perception (Surprise)
Only needed if you want to automate rollling for surprise.