Dodger,
1) Average take home will vary with seasonality. FO takes maybe £3100 after pension and a good month, SFO maybe £3400. Winter will be less.
2) Command requirements are 3000 factorised hours, 6 months post Final Line Check and 300 hours on Jet2 aircraft. If you're coming with hours, then pretty good, however it can take time when you're only doing 550 hours a year (although seems to be more nowadays)
3) Yes. Although apparently it's been capped now so if it takes an unreasonable amount of time due to no fault of your own you will go to normal pay.
4) Good-ish. Summer is hard work, expect 6 on, 2 off. Some duties separated by less than 62 hours (quarter day off payment for your trouble - DOP for FO is £250, Capt £400 before tax). Aircraft seem to have their fair share of tech problems, meaning some work out of other bases, and the inevitable Airport Standby messing about. Otherwise a friendly place to work with a good range of experience and nice crews.
5) GLA is 800 only on the 737, EDI is 300. EDI does night mail, GLA does the longer flights, so it's 6 and 2 x 3. Longer flights mean more duty hours = can't do as many flights. However we worked hard in the more southerly bases this summer (see above)
6) Probably. Company has stated the 757 will hang around a bit, and rumour is they are leaving NCL to go to LBA and the 800's are going the other way. Long term I think the plan is to get more 800's.
Good luck to you. The recruitment gears may drive slowly, but you should get an answer eventually!