Very tidy and nicely laid out!
You already got some good advice on the battery, but here is even another one: :-)
I have this battery in my excavator. It's quite cheap and small while still at the 3S 5200 mAh capacity and costs only $19:
MultiStar 3s 5200mAh
(Mine has a XT-60 discharge plug but the Amazon text reads XT-90. I believe that is wrong.)
Best regards,
Stein :-)