Hi there knakered
Good for you - I wouldn't bother about doing slimfast until you start as those 100 days are pretty tough on you but SO worth it.
Just carry on as normal until you start, but cut out carbs so you don't get a carb withdrawal problem during your first few days on LL.
As far as the counselling goes - I was a bit worried about the same issues as you, but now, having done it, I found the 2 hour sessions EXCELLENT.
obviously, it depends on your group, but you will all be women and all have a weight problem. You will be different ages and from diffferent walks of life, but that actually helps.
The first 30 mins or so is just the weigh ins (which is done one to one) and the rest of you just chat - this is brill as you can talk about how you are coping, etc.
Then, you watch a cheesey LL DVD - tailored to where you are on the programme. It is quite annoying but you do learn stuff. Then, for the remaining 50 minutes, you work as a group with your counsellor, using your foundation book to go through what you heard about in the DVD.
The time flies by and yes, it can get emotional but everyone is UNBELIEVABLY SUPPORTIVE. Often, you don't realise things about yourself until someone else says it themself and then you think - blimey, thats what I do/did/think/etc and all of these contributions help you change your way of thinking and that is what is key to keeping the weight off.
You can do one to one via Cambridge but I know lots of people who have done both and although LL costs more, you are paying for this 2 hour group counselling.
It will all depend on how your group bond but after week 3, it is a closed group so noone can join. It is always single sex.
Our group bonded amazingly - we had a laugh, there were tears but noone dropped out, we supported each other all the way and I have made some lifelong friends out of it.