Hi Patrick,
I'm using a Pivot 3 throttle and cruise controller in my 2003 M35 VQ25DET, and it works well. I didn't care for the throttle controller function so I can't comment on how well that works, I only bought it for the cruise control function which is great.
https://pivotjp.com/product/3da/3da-e.html
As for the fuel flap lock, there is a lock actuator behind the fuel flap lock mechanism that I believe prevents the flap from being opened while the car is locked, but mine if disconnected because it's broken so I can't be 100% sure. You have to give the edge a gentle push and it will pop open. Not really the answer you are looking for I guess.. hahaa!