Juud,
There are 3 fleets in what we call "Mainline" (not franchise etc). Worldwide (long haul only) and Eurofleet (short only) - both at LHR. Single Fleet is LGW, mixed flying. Within each fleet, there is old contract and new contrac, ex-dan air contract, ex-cityflyer contract and ex-eog contract. Confused yet? So am I.
As I'm at LGW I can only speak for our allowances. We have basic, then hourly pay from check-in to check-out. A set amount per night away (peanuts, honest). Two days off after a long haul as minimum. "Overtime" (slight increase on hourly rate) after a certain amount of hours.
At LGW, most crew (apart from Cabin Managers) have 3 aircraft to their name: B737 (3 variants), B777 (2 variants) and A319/20/21. The reason we can have the 3 'buses on 1 licence is due to doors being the same on all of them.
On short haul, 1 supervisory grade (can be Purser or CM). On B777, we have 1 CM and 2 Pursers (for now anyways, we're threatened with one being taken off).
We have restrictions as to how many "earlies" you can do and how many "night flights" you can do, but it doesn't incur extra payment.
LHR fleets have a completely different allowance system, and tend to earn quite a bit more than LGW for doing the same job - whence the disagreements between bases sometimes, although most of us just get on with it. It's only when riled I get involved in the discussion.
We have a bidding system on LGW and EFLHR. Part time is guaranteed if you have a baby (although only for the mother). There is a list you can put your name on for part time, but the waiting can be endless.
I hope this answers some of your questions.
Gg