The esc comes in the package with a low ESR electrolytic capacitor that needs to be mounted close to the ESC LiPo pads and the capacitor wires need to be as short as possible. Ideally you want the capacitor soldered on the LiPo pads after main power wires were soldered. If space is a problem and capacitor needs to be mounted farther away then extending capacitor wires to the ESC LiPo pads is acceptable if using short(max 20-30mm long), thicker sillicon wires. Mounting the capacitor on the XT60 is not recommended because the effectiveness drops.

To be able to update the ESC firmware you need to use the KISS ULTRA FC GUI: www.kiss-ultra.com

Yes, Voltara 70A ESC is capable of effectively spinning the motors from 3s up to 8s voltage (33.6v).

Yes, since Voltara 70A can receive Dshot signals ranging from Dshot150 up to Dshot2400 any FlightController providing Dshot signals is compatible. Betaflight can effectively change motor rotation from its GUI motor direction wizard and read the Telemetry which contains Voltage, Current, mAh used, Temperature, RPM, etc. Voltara 70A does not have a Bi-Directional Dshot and that means losing the RPM filter in BF.