I don't know about places to eat/stay, but smoe basics (and probably things you already know):
But FIRST & MOST IMPORTANT: RELAX - (you and your husband). Your son is going to pick up on your 'terror' .....
1) Try to arrange your arrival time by mid-day. This will give you all time to settle in to your hotel and get familiar with the town and it's opportunities for entertainment.
2) Limit SUGAR - especially after 2 PM. It only aggravates ASD and ADD children (& adults).
3) Be sure to take along some of his favorites - toy, pillow, blanket, DVD, .... and buy a NEW toy or game or movie - something he will associate ONLY with a vacation.
4) When you first arrive, look for a favorite restaurant (of HIS) - McDonald's, Whataburger, Jack in the Box - someplace he will connect to being home .... try to eat your first meal there.
5) If he likes the water, make sure the hotel has a pool and spend some time in it with him.
6) Buy him a beach package (sand bucket/tools, etc). If he has never been to the ocean, he will probably find the beach really scary. Let him play in the sand and build a sand castle or something with him....you may go 'wading' but do NOT force him into the water - even if he is being held .... (it's sort of like forcing a kid to sit on Santa's lap when they're terrified of Santa).
7) He will probably not be interested in going 'shopping' - so if you are going to take back souveniers, let him help pick-out gifts for Grandma & Grandpa, etc. You can pick out a few and let him choose which one (sort of like you do his clothes...'which one do you want to wear today?).... OR, you can point him toward a certain section (cheap) of the store and let him pick out something on his own .... give him the money and let him actually buy it. (if it isn't what you had in mind, one of you stay with him at the hotel, pool, etc., and the other go get the gift you had in mind).
8)If you want to do a nice, relaxing seafood dinner on the beach, be sure they have American food - burgers, chicken nuggets, etc ..... in case your son doesn't like seafood. (A lot of restaurants have books/pages and colors for small children. Just in case they dno't, you would do well to bring/buy one .... these things will keep him busy while waiting for dinner .... (snacks-crackers, etc - are always good to have in your purse,
too).
9) If you normally attend church as a family, try to attend at least one service ....
The key to this vacation is two-fold: try to include things he would normally experience at home and try to make the 'new' things really interesting for him. As best you can, try to keep his routine as close as possible to his routine at home (meal time, bath time, bed time, etc.
Second: Wear him out .... the more activity he has, the more tired he will be and ready to go to bed and sleep well. A good night's rest will help him cope with the new stuff.
Good luck....