Hi
In answer to your questions,
1) Depending on duty pay, somewhere between 2k and 2.5k UK pounds a month after tax.
2) Almost certainly.
3) Work 20 days in every 28, of which up to half may be standby. Standby periods are usually 6-8 hours, with one hour allowed (2 at LHR) to report after they call you. Duty pay is at the same rate for standby as for flight duties.
4) No
By the way, yes, but JB has a large stack of applications to deal with, so you might not get a quick reply. You need to be in current flying practice, and try and have all your licences and ratings current.