I would not encourage giving too much "stuff" or any money up front. We did that for our first au pair, and it really wasn't appreciated.
Yes, I would provide a nice, but basic room. We redorated the bedroom, bought a new double bed, new sheets, duvet etc., and provided a TV/VCR and DVD player. Also basics like coat hangars, laundry basket, wastepaper bin and mirror.
We gave our au pair a mobile phone as we wanted to be able to contact her, or her us (lack of English made this impossible though). I provided a few phone cards - an initial one would have been fine though.
I think if perks don't cost you anything, then fine, let her have use of them. But don't expect anything in return.
I think it is reasonable in the first week to take her out to lunch or into London.
Use of the telephone is something to be clear about. I think it is reasonable to let her call her mother when she first arrives, but after that, she should pay for her calls. If you let her have free use of the telephone, she may well abuse it (the cost of my old au pairs calls were 10X the amount for the rest of the family).
Based on my experience, I'd say it is better to be strict up front, and then to relax once you get to know her better. A lot of families will promise the au pair a sizeable bonus if she stays for the agreed time frame, which I think makes a lot more sense than a golden hello.