I am planning on having my wedding at Dreams Cancun in July 2012, I haven't booked up yet but have received so much information from this forum and from reading other Dreams Cancun brides reviews. From the information that i have gathered I will try and answer your concerns.
With regards for music for the ceremony most of the past brides have suggested putting your ceremony music onto one CD in the order that you want it played. They have a sound system at the Gazebo (is this your chosen ceremony location?) and apparantly the WC at Dreams has a headset on and she communicates with the sound technician through this telling him when to play the next song. I haven't come accross a brides review yet that said this didn't work out well, they all said that the music flowed perfectly and the timing of the technician was great.
I know that alot of brides bring their own decorations with them, but the WC does have a meeting with you when you arrive at the resort and goes through everything in detail, all of the brides on the reviews that I have read have said that this is a great help and put their mind at ease straight away. They were able to tell the WC exactly how they wanted the arrangements for the decorations and also choose additional decorations if needed. when you arrive at the resort request to see your WC and she will usually arrange a meeting with you the next morning.
Regarding your hair and make up, i have read by many brides that the best person for this job is 'Christian', most brides contact the spa before hand to request that Christian do their hair and make up, he is supposed to be great and all you do is bring a picture to show him how you'd like your hair and he'll work his magic. So probably best for you to contact the Spa asap to request him.
I hope this has helped to put your mind at ease...I know it's easier said than done, but don't worry Dreams do weddings all the time and they all look amazing and I'm sure yours will be everything you ever wished for.
Don't forget to post your review when you get back for all us future Dreams Cancun brides.