7.4v is 2s not 4. Battery might be wired 2 series and 2 parallel for higher capacity.

The 5700 castle setup is a basher setup it might be fine if you are racing a non restricted class like novice. You will notice some low speed cogging when starting because of the sensorless setup of the system. Your castle esc should have auto voltage cutoff to stop you once lower voltage cut (LVC) is reached.

Make sure to use 7.4 or 2s charge voltage and lipo mode when charging that lipo.

Gearing seems to be a good starting point with the 5700 kv motor.

Also checkout the rookie zone for beginning questions. Might help.