I am with you with that. I hate, hate, hate not knowing in advance how things are going to work. I need to know the fine details and where ds1 is concerned I need to make sure he knows as well.
Sympathies on the nursery home visit as well. Dd had hers yesterday. Two whole blooming days of cleaning and sorting the house with a broken foot and gastritis for them to come for 15 minutes. 
I even baked chocolate brownies for them, despite not being able to eat anything but porridge myself for the past fortnight.
We are midlands and he is going almost to West Wales-ish.
I am not confident of them handling things and informing the centre properly. I had a meeting with the lead teacher at the end of last term and gave them briefing notes to accompany his passport, but if this week's return to school is anything to go by, they won't have read - let alone actioned them.
Yesterday he came home to tell me that they had put him in a different group to his best (and really only) friend and that another boy had been put in a dorm on his own! Apparently it was all sorted out (reading between the lines, ds1 gave them little choice) but ffs, they know that his best friend acts a a sort of social guide dog for him and the school has always made sure they are together. On top of that they managed to put one of his old bullies into his bedroom - despite me specifically reminding them not to.
The only saving grace is that the centre is used to running residentials for children and adults with a wide range of disabilities, so I know he will be safe, as long as I can make sure they are properly made aware of his difficulties.
I am also fretting about the fact that he won't have his Nintendo DS for five days for destressing and that he isn't taking his beloved cuddly and angel, which he uses as part of his bedtime ritual and can't sleep without. He has such a specific bedtime ritual/routine, that it would be impossible to replicate on the trip and without it he simply doesn't sleep.
He is really excited about going, but developing more and more anxieties by the hour. Last night he was still awake at midnight and again at two, then awake by 5.30 am. Of course it didn't help that his new maths teacher kept him in at break, as a punishment, to finish his maths test yesterday. This was all supposed to have been sorted and agreed last term. There was a staff meeting involving last year and this year's teacher and the HT when they were told he should either be allowed to do as much as he can in class tests and will be given additional time for tests and assessments AND he should NEVER be punished for not completing classwork. On top of the processing issue, it was copying problems long-hand and they know that's something else he can't do due to visual and handwriting issues. 
Of course if they'd read his bloody statement they'd know all this - but when I asked the other day, the teacher didn't even know he had one.
I am going in to speak to his teacher after school this afternoon.