Hi BAL
There are no precise answers to your questions, but I'll give you some figures to think about;
- rent around LHR area will be around £300 at least, bills may be extra. The area around LHR isn't that nice to be honest, with Windsor being the only notable exception. It's definitely worth coming down to have a look. Don't worry too much, you'll find someone to look with during your training course.
- take home pay varies a lot, depending on what your roster looks like. If you're not flying that much, you may only take home around £1200/1300. But on a busy month, and having opted for some overtime duties, some people are taking home £2000. I average around £1500/month which is not bad for a job I love.
- promotion-wise, nothing is set in stone when you work for an airline...that goes for everything really! At the moment, promotion is more rapid than it has ever been at BA, since loads of people are retiring. By "rapid", we're talking 3-4 years to Purser, although this may lengthen; a lot of people don't think it's enough, but that's because in the olden days it took three times longer to become a SCCM at BA. How fast you move up the payscale depends on your status i.e. whether you're main crew or SCCM; bear in mind you'll join on the 'new' contract, so you'll never earn as much as the grey-haired CSD's that joined 20 or 30 years ago!
- 95% of the crew are very easy-going and fun to fly with. The great thing about BA is that you get all sorts - from ex-flyers to novice flyers to people who hold Masters degrees. There's something for everyone, and most people enjoy work. That leaves 5% who spend most of the time moaning and being negative, don't like the changes since they joined, or simply outright weirdos - thankfully there are relatively few!
I hope I've given you an accurate and balanced view of what you can expect.
Let me say this; as far as airlines go, it's definitely one of the UK's better companies in terms of job satisfaction. Modesty aside, it's GREAT! You're gonna love it. Nice uniform, mostly nice pax, great crew and some fab nightstops not to mention the great staff concessions.
Enjoy.