Duration of trip/stops: no limit beyond what is legally ticketable. I think this is something like one calendar year.

Stops vs Open-Jaw: You are allowed a turnaround point, plus two stops. If you want to use an open-jaw, I think it removes one of your stops and it must be either at the start or the turnaround - meaning your start point, or your turnaround point, must be included in the open-jaw.