I'll let someone from shorthaul answer the pay and roster questions, As far as the rest goes:
Expect a longhaul FO position (777 or 747) after five or six years. For the first five years of employment, you are likely to be type frozen although BA can move you if they choose. Once that freeze is up, you can bid for longhaul in line with whatever seniority you have at the time. If there's a vacancy and you're senior enough, you'll get it.
Commuting will be possible eventually. Keep in mind you won't get staff travel for your first six months and then when you do, boarding priority is based upon earliest date of joining irrespective of whether you're a pilot, cabin crew or anyone else. You will also have to do Reserve (standby) probably for one month a year. Shorthaul involves some airport standby and some home standby. For home standby, you are required to be two hours from the car park. I would suggest you would need somewhere to stay around London for this time if nothing else.
Staff travel, which you will be elligible for after six months applies to you, your partner and kids up to the age of 24. If you don't have a partner, it applies to parents and brothers and sisters up to the age of 24, or a "Travel Companion" who can be anyone you like, although they can only travel when you are also on staff travel tickets (ie. they can't go on trips with you).
As for the new pension, the less said about that the better. As you know, the Final Salary Scheme is closed to new entrants. There are better Money Purchase pension deals out there with other companies.
Hope this helps.