Hi, from what I remember about employer references on the application form, you need only detail the last five years as that this what BAA require to organise your airside pass. If you've been in the same job ten years, don't worry about previous employment.
You need excellent spoken and written english skills so if you speak as well as you write you've nothing to worry about there. You won't need to provide any evidence to support your application as that will speak for itseld I think.
You won't be entitled to any staff travel benefits until you have passed your probationary period which is six months. If your probation was extended for any reason (like excesive sickness, pax complaints etc, it does take a lot for them to extend it so I wouldn't worry) then you wouldn't be entitled to your travel benefits. It would be a lot lot lot easier to live in or around London for your first six months as it's a mental job to try and get used too and I know from my experience I really wouldn't have wanted to commute then! Now I do a two hour drive to and from LHR but I really don't know if I could have done that at the beginning. From your point of view paying full fare tickets to get to work will probably end up costing you more than you earn.
I hope this helps, if you've a any more questions please do ask. Good luck