I'd stay away from deans if you already have bullets, no need to introduce another connector into the mix.
If you're going to have mixed bullet sizes, I'd put 4mm on the speed control and put 5mm to 4mm reducer sleeves in your 5mm packs.
https://www.amainhobbies.com/protek-rc-5mm-to-4mm-bullet-reducer-2-ptk-5005/p14566