Great choice on components. Since you are planning on using an external 2S receiver pack, there may not be much value to using the CC BEC Pro. The MKS servos you are using will run very well on a 2S LiPo. The BEC Pro would be a better option if you were planning on powering the electronics with the flight pack. Whatever option you use to power the electronics, considered using a 4700uF capacitor connected to either the FBL unit (the theoretical better option) or the receiver.