Hi, Alisa! Congratulations to your son on his First Holy Communion! We just went through that this past spring with my daughter, and it is an incredibly special time for them!
The best thing you can do is really get your son involved in planning the vacation. Take him to
www.disneyworld.com to let him check out the attractions at each park, and come up with a game plan of the things that would really make his trip amazing. You can also see all of the Walt Disney World dining experiences there, so you could browse those with him and see if there is someplace special he might enjoy. Many boys this age like Whispering Canyon, Donald's Safari Breakfast, or even the Sci-Fi Dine In at Disney's Hollywood Studios.
If he's a fan of pirates, you might take him to The Pirates League for a pirate makeover, followed by the Pirates and Pals Fireworks Voyage. The Pirates League is located at the Magic Kingdom, just outside the Pirates of the Caribbean ride, and you can do just a pirate face painting thing, or get the full pirate outfit (I would buy a size larger to hang onto it for Halloween next year!). The Pirates and Pals Fireworks Voyage leaves from the Contemporary Resort, and after a scrumptious buffet of all kinds of snacks and drinks, you depart on the Seven Seas Lagoon for a front row seat to the Electric Water Pageant, followed by the most amazing view of the Wishes Fireworks from the Magic Kingdom. You'll get a couple of character meet and greets thrown in, to make this a really special occasion.
I hope the vacation is wonderful, and God Bless your son as he prepares for his First Holy Communion!