Hi Leslie, How fun to planning your sons first Disney vacation!
Since you mentioned "moderate", have you checked out Disney's Moderate Resorts? See:
HERE. Of those properties, I would recommend Disney's Port Orleans French Quarter. Doubloon Lagoon—the pool complex—includes a waterslide that resembles a giant sea serpent (see photos on the link above). He may enjoy the pool at Caribbean Beach Resort, but that is a very large Resort and too spread out for my liking.
I have a 9 year old son who is very into sports and he loved the theme of Disney's All Star Sports Resort. See:
HERE. This is a Value Resort and doesn't have a slide though. If it's an option, I would recommend a Moderate or Deluxe Resort for you.
A few suggestions for meals would be:
CHEF MICKEY'S,
'OHANA for dinner and
DONALD's SAFARI BREAKFAST.
Your son will find things that he enjoys at all 4 Parks, and I'd suggest that you spend at least 5 days if it's an option. Due to space constraints, if you'd like to send me a follow up question regarding rides and experiences for an 8 year old boy, I'd be happy to help you. Please be sure to let me know what your sons interests are (ie: Star Wars, Indiana Jones, Pirates, Sports, etc).
Hope this helps and have a wonderful trip!
Kaylene