We've been both times, and I would suggest Oct, too. The decorations are wonderful and he would love the party, if you can swing the extra cost. You'll have a great time, I know!
As for saving money, here's a few suggestions to consider:
-limit snacks and drinks. We toss a small bags of nut, granola bars, and some hard candy in our bag and carry a small plastic water bottle and fill it from the water fountains. If you dislike the taste of the water, you can ask for free ice water at QS locations.
-share QS meals. We find the portions to be large and very often split a burger and fries or sandwiches.
-limit your ADRs. Most TS is at least twice as expensive, usually more, compared to QS. A character meal would be fun for your child, but don't expect him to eat much!
-eat breakfast in your room. We take instant oatmeal and juice packs, fruit cups, muffins, etc and eat before leaving the room.
-limit trinkets. Decide ahead of time what your son can buy to avoid arguing over purchases at the park. Maybe draw them on paper and he can mark them off as you go: a t-shirt, a toy, a hat, etc.
-buy glow in the dark stuff at the dollar store, skip the park night time toys.
-check your HR office to see if they offer discount tickets.
To plan:
-once you have your reservations, check park hours, EMHs, and plan which park for which day. (I plan it on paper) Then, make ADRs and FP+s for each day.
-check parade times, show times, etc and note them. If the parades and shows are very important, you can plan ADRs and FPs around them.
-set up a My Disney Experience account on their website and WDW app on your phone. From both, you can save favorites, etc and change FPs and ADRs easily. Check out the app before going- it provides lots of info and options and it is easier if you know how to use it before getting to the park.
-plan a long break during the middle of the day and leave the park for a swim, snack, and nap for both of you.
-take some time away from the parks to see other things in the area. AKL is wonderful and has a great viewing area out back- it's a peaceful place. Your son might enjoy riding the monorail out and back to Epcot, just for fun.
-familiarize yourself with the parks' layouts by checking the Disney website maps and Google maps.
-check the website for info about height restrictions and what rides are appropriate for your son.
-prepare him ahead of time for what to expect...there are rides for big kids and adults that he can ride when older, but there are many fun rides for him to enjoy.
