Factor number 2, the aircraft stall speed, has been mentioned so far only in passing. Weight obviously affects this and handling qualities dramatically.
A Super Cub one-up with half tanks is a completely different aircraft to one which is at gross weight. Bush pilots operating Super Cubs in and out of marginal strips will go in with minimum fuel and top up by 5 gallons at a time, as needed. On my Super Cubs Hardcore video (!) there is a grizzled Alaskan fellow who operates a 180HP Super Cub without an electrical system to achieve max power to weight ratio and minimum weight.
So important is weight that I would qualify Factor 2 to read: "Aircraft stall speed and weight."
QDM