Jon,
It may not be clear from your OP what information you really need. The information you say you want might be different from the information you really need. The majority of FIs working at flying schools are self-employed freelancers. As such, they are all always looking for work.
Your typical UK hele flying school tries to transfer much of the risk to other people. So they lease in aircraft and use S/E freelance instructors. They expect the instructors to do a lot of the marketing too.[This is not a pop at schools - it is just a recognition of the reality of trying to break even in this business].
Any new FI will have to work hard for every hour of paid flying. As others have said, the only way that normally financed people can earn a living is by sharing FI work with another source of income.That other source will have to be flexible, to allow you to take up any offer of instruction, whenever and wherever it comes from.