If you are going to use bullet connectors then just stick the castles. 4mm should be fine for anything 1:10 scale. If you are running a "monster" type motor then I would get the bigger castle bullets.

Do not use the 4mm birdcage connectors, they are very hit and miss with folks and some of them have more resistance to them and they get hot as you draw current through them.

If it is an option for you then just do a direct solder to the ESC, no muss, no fuss... but I know that does not work in every playbook out there.

Any (battery and motor) connectors, wires or solder joints you have should get a baseline with the first few runs at least. If something is getting hot, address it... if you are using good connectors then more than likely you have a solder issue going on.