Most groundschool instructors have significant experience in the aviation field. Not always as pilots (although some do) but as other aircrew or engineering related trades.
You wouldn't be on a particularly strong wicket without some depth of aviation related knowledge to fall back on, although it is not a necessity. I did that for several years during the early 90's with a engineering degree to offer as the basis for teaching electrics, but I was already working at the school in question as an AFI so I was a known commodity
Its a bit of an assortment of lost medical folks, mostly fairly aged, and often ex service, with the odd youngster thrown in.
Regarding your conventional teaching background - its a very different kettle of fish. The pupils are highly motivated so a lot of the normal workload associated with keeping them on task is reduced or absent altogether. But bear in mind you may have extremely experienced pilots, either foreign licence conversions or ex-miltary chaps who will expect you to have deep knowledge. For the less experienced students, giving them a useful education as well as teaching them to jump the exam hoops is the mark of the expert.
Offering several subjects will help, many guys are 1 or 2 trick ponies.
Pay? Can be reasonable. I'm a bit away from it now, but in '96 I was on 24K. I understand OAT pay about 32K now. As for other schools, I can't say, but I would imagine there is a wide range at the bottom end.
Job opportunities? Theres a bit around at the moment, but probably more schools offerring the training than is long term sustainable. But you also have an aged workforce so there is a need. But its very niche. I don't know, but maybe 50 guys in the whole country?
It was remarked to me recently that recruiting ground instructors is difficult. Quite a few applicant, but weak.
I hope that helps a bit. Where did you do your groundschool? Frankly its a who you know situation.
CPB