Regarding not being paid when not flying -
A few years ago the Inland Revenue (UK) ruled that all the time an instructor was at his / her base or airport they had to be paid at least the minimum wage. ie if you spent 6 days a week 8 hours a day + all November hanging around the flight school waiting for (a) a student (b) some weather that was remotly good enough to fly in and (c) a servicable aircraft but only flew 2 or 3 hours and your employer only paid you for those hours you have probably bin robbed.
Also some companies will require you to get permision even if you are not paid when instructing.