Providing the terminals are 100% the exact same type on the FrSky module and the Assan pigtail, it will be fine.
With these systems, the only critical part is the length of the actual antenna end length, as it tunes to the 2.4GHz. Extension cables can be any length theoretically.
I'm sorry to hear this. Please open a support ticket here and we'll take care of it:
The transmitter has failsafe settings, but, if you are using the stock receiever that comes with it, failsafe is not supported with that receiver.
The original 9X transmitter from which yours is derived, had failsafe when it was a PCM 9 channel set, but now it is 2.4GHz 8 channel PPM, it does not operate.
You would need to purchase something like the FrSky DJT module and D8II series receiver to permit failsafe.
KV relates to motor revolutions per volt. For example a 3200KV motor rotates at 3200RPM per Volt. That motor powered by a fully charged 3 cell LiPo could (theoretically) spin at >40,000RPM.
75-80mm from the leading edge of the wing.
or maybe this one
Bixlers can fly pretty slow too: