You will get given a bus ticket with a time on when you register to help prevent everybody arriving at the same time. I doubt it matters too much if you're not there at that exact time but it will get busy.
You can always take a portable USB charger and charge up for an hour or so half way through. That said I don't think I'd bother for this race, knowing how far to the top would probably demoralise rather than incentivise! On one climb I remember thinking I must be about to summit for a good hour before I actually made it to the top.
The problem with reps though is you just don't get tired like you do on the long climbs in the Alps. Mentally knowing you've got a 2-3hr constant climb coming is quite draining too where as reps (at least round my way) are no longer than 10 mins max. My best training day for CCC was probably in Brecon, doing as many long topbottom loops as I could.
I think whatever you do so long as you put the time in you'll be fine. Unless you're a keen racer I would try to forget about the clock and just try to enjoy it as much as possible. I started right near the back and a very steady run meant I was overtaking the whole time, nearly 1000 places from first CP to the finish! Having something you can eat at all times will help too. It can get quite hot in the day and quite cold at night so your body can get a bit messed up, I was surviving on noodle soup and oranges mostly, which towards the end wasn't giving enough calories.
The same goes for any night ultra, but if it's cold at night try and be quick through any indoor aid stations (of which there are quite a few on TP). You don't need to stop for long to really feel the cold when you go back out and if you're down to a shuffle then it's hard to get warm again. I was on CP duty at Whitchurch last year and it was carnage with the number of drops. Quite a few left and came back 5 mins later shivering.
Sticking with that, recognise that this is what's happening when you do start shivering after an indoor CP and keep moving, you *will* warm up again within 5 mins if you can keep the effort going. Don't let your brian use the shivering as a way of talking you into dropping!
I reckon you should seek advice from a professional rather than asking strangers on the internet. You've got no idea who anybody on here is or what their experience is, nor do they know much about your background. It's too easy to follow the advice you like the sound of but really you've got no idea if that's going to be suitable for you. Completing the challenge obviously means a lot to you, so spending whatever on a consultation with a personal trainer has got to be money well spent.
I would echo what Peronel said, spend the next few months finding answers to those questions and you'll be giving yourself the best chance. In addition to that I'd say you need to get your VO2 max as high as you can, being physically fit will make it so much easier. You really want to avoid injury too though so do lots of different things (gym?) rather than just fast running. Again, a PT will know much more about this and should be able to give you a plan to follow.