Hi there,
I am not ex mil but I do have some things to offer.....
1) ATPL groundschool. Yes you will be exempt from most of the exams. I believe LASORS (just search the CAA website) has all the info you require. I went to Bristol and found it SUPERB. There were lots of ex mil guys doing the bridging package and they found it very suitable.
2) IR - I believe there is a company based in either Exeter or Bristol that offer good rates for ex mil people. Someone that has followed ths route might be able to help you there. Same with the MCC...
3) Jobs. It depends on what you want. I can't offer help on which airlines are pro versus anti ex mil guys, specifically ex FJ pilots. To be honest common sense would suggest that 10 people could argue that airline X is pro and airline Y is anti. However, in reality it makes bugger all difference as it is the Chief Pilot/Recruitment people that decide that.
Regarding timing - Most airlines in the UK, ie charter types run courses in the new year in order for you to get onto the line by the summer season. This is not the case with every airline but its a good starting point. So this being the case, apply around early summer, airline review applications over the summer and hold assessments/interviews (depending on thier assessment processes) towards the end of the year.
Hope this helps