I have gone through it, and I have a very similar situation.
WiFi/BT card:
Airport Wifi Bluetooth Network Card For MacBook Air 13" A1466 Mid 2013 Early 2015 BCM94360CS2 802.11AC. Chipset:
20702B0.
My WiFi and BT were working perfectly on Sierra: Handoff, Airdrop, BT keyboard, BT mouse, BT...