If he is super into Disney Transportation, I would say start by planning a whole day of riding every kind of Disney Transportation you can find, and you won't need a Park ticket for any of them.
Buses - They go to and from the Parks, obvs
But, you can also go to and from Disney Springs and other Resorts, and you can use the Parks & DS as "hubs" to get between them.
Boats - there are many different kinds, as you well know - Off the top of my head, I can think of 3 types that don't even require a theme park ticket! From the water taxis at Disney Springs (and you could even travel down the Sassagoula and have a meal at Olivia's at OKW) to the Friendship boats that run at/between Epcot and HS, and what I think of as the "old school" launches that make the run from WL to MK (the smaller boats that run from WL to CR & Poly to MK have a step down and would require a transfer as well as his chair being folded and carried on board, down 2 steps, not recommended)
Skyliner - It is fully accessible, and quite the ride. Ride it both at night and in the daytime to get the full effect.
Monorail - an Oldie but a Goodie! Of course, a CM will deploy a ramp for the chair, no biggie, and (to me) it's every bit as cool as it was when I rode it for the first time back in the 1970s!
Golf Cart - OK, this sounds weird, but you can rent a golf cart out at FW, and go exploring all over FW in the cart! Its most cool and amazing at Halloween and Christmas, when everyone decorates their campsites, but any time of year it's so pretty out there, and everyone is just so nice.
Balloon ride at DS - go up in a (tethered) balloon - provided he's OK with heights. (I'll be over there, taking pictures from the ground, thanks! LOL)
Don't forget that POR may have the horse-drawn carriage rides, and FW may have hay rides by then also; BW has the rental pedal-carriage-bike thingys, too.
And as for the Resort, well... he's not into animals, but if he is into watching boats go by, y'all could eat every meal at WL down at Geyser Point, and sit by the lake. The lighted water parade still runs every night, too, and they stop by WL. I love BC, it's so pretty, but I have always felt like WL/Copper Creek has a more laid-back relaxed vibe that might be better for a kiddo. If you really want adventure, you could always stay at the Treehouses - that's on my bucket list for sure! I would love to be able to stay in one of the units by the river, and watch the boats come and go; we love to ride the boats at WDW, so it would be right up my alley! I also think that it would be amazing to stay at Poly in one of the over-water units, but you while you could see the boats (and the fireworks from MK) you wouldn't be able to ride them.
I would say focus on what your plans outside the hotel will be first, and that might help inform your decision about where to stay!
Let us know what you decide!