Hi, we went a few years back (DS 8 at the time has autism). We didn't stay in the disneyland hotel though.
Only advice really is to take evidence of diagnosis with you, we also asked the GP to write an accompanying letter. If you show that to the staff they will tell you where to go to get passes, which means you don't have to queue at rides/attractions. This was brilliant for us because DS could not have stood in line to queue as he can't handle being surrounded by lots of people (some were waiting nearly 2 hours for 1 ride).
It does get packed there, which you need to be aware of. Also there is one ride .. in universal.. can't remember what its called sorry, but they show you special effects etc and its brilliant... but a lorry does explode and water does go over the carriage which you are sat in, DS freaked out and tried to get out, we did stop him but he wasn't happy with it, so if your child doesn't like loud noises just be wary of that one.
DS and our other two children did love it though (it was the first time we had stayed overnight anywhere too, we expected him to be unsettled but although he was a bit at times he did very well) and I said to my husband at the time we should of stayed in the disneyland hotel because also DS does like watching fireworks, he doesn't like the noise, and as the disneyland hotel overlooks where the fireworks are set off from its ideal :)
The Peter Pan ride is lovely btw, and was DS's favourite.