I'd say that you really might want someone to go with you for your surgery if possible. Most surgeons, certainly Levick and Karidis put you under GA, some people come round fine others are a bit groggy. Levick has the advantage you'll have had near 24hrs to recover in the hospital, but still you won't want/be able to drive home. I've heard of people getting the train, but from my own personal experience I wouldn't wanted to travel alone, just having a bag or suitcase would have been difficult, and I wouldn't have wanted to be going through stations and one and off trains afterwards. I guess it depends how far how many changes and such.
The price is high, but you have to remember what you are having done. With Levick, you are going to be booking out a room in a private hospital for 2 days and the equipment like the pumps, you are going to have to pay for use of the theatre, the nurses and staff that come with it, you are paying for the anaesthetist to put you under and monitor you while you are out, and finally you are paying for a surgeon in Levick. All of this is coming at private medical prices, pretty similar with Karidis, but he's in London so even more pricey. You can probably get it cheaper, but obviously they have to cut corners somewhere.
Main difference between Karidis and Levick is location and hence price, and beyond that the technique. One of the other things to bear in mind is Levick does free revision work, not many people seem to need it but its worth bearing in mind especially if you know you might be more prone to have issues like loose skin or something. I don't believe there is any difference in the quality of their work.
As for the OP, not really much you need to take. Remember he's going to want your shirt off, so probably wear something easy to get on and off. He wanted some of my GP's details, so if you can't recall them probably check them before you leave. He gives you a little pack to take home with information and a pamphlet for the vest which is the only other cost you need to consider beyond getting there and paying for it.