I'll try to answer with what I know/read.
A FGIT just posted that the only deluxe dress they have right now is the Belle red dress.
Before others were, like the Ariel wedding dress, or at least I read it was, but I bought one last week and it was only $64.95 like all the other dresses.
Yes the age limit is 3. I think I read a few who got there children in who were maybe less than a motnh a way from 3, but no earlier. We booked our 3 YO last week and she was excited, but the ngot the flu while we were down there and when it came time for the appointment, she wasn't having any of it. So we didn't push it. Some kids just aren't even ready at 3.
Crowns come with the castle package, as you get the crown to go with the dress you pick, I believe. The bun hairstyle comes with a crown no matter which package you do. It's a small tiara. Yo ucan buy it to add to any other style yo upick though. We bought one at World of Disney. (actually 2, becuase DD lost her first one after a couple of days.) They also sell extension type ponytail things if you want to buy them, which we did, since DD wouldn't let them touch her.
One question on the extension. I am trying to figure out how BBB puts them in. It is on a think like a pony tail holder, but honestly to twist it, would realyy mess up the look of hte hair. I just put it around her ponytail, and it was very lose, and secured it in place with the tiara comb. Does BBB use pins to keep it in place or do they twist it?