Oh wait. My previous reply - I wasn't even aware... this kit doesn't even have a motor. Hope you can swim 😅
But you won't be using an ESC. So the power switch will go between the battery pack and receiver.
I'd hook it all up outside the bost and get things all figured out. Post a pic of all...
The switch turns on the ESC, which in turn feeds power to the other electronics. The motor gets the full battery power while the Rx (receiver) is fed power via a JR (servo) connector via the BEC (Battery Eliminator Circuit) in the ESC. The BEC steps the voltage down to a level your Rx and servos...
Spektrum - I'd almost bet money they use their own stupid tooth count for the servo gear. Like I said, I have no experience with 5th scale servos though.
I would recommend you count the teeth in that long sail horn so you know what servos will fit it.
Another thing about Spektrum servos, if...
Looking at the manual, it suggests a servo, but it's hard to find it.
Looking at the exploded view, it labels the servo as part 54
Looking at the part list it gives you a specific servo model number, which is KS501SW
Looking at the servo dimensions, you get
So yeah. You're looking for a...