The AIM does calculated gear from speed/revs, gear input from a gearbox pot or gear from the ECU.

I run a pot on my gearbox which makes it easier and more accurate, but not sure if or how you would do that with a T5 box.

The dash can display fuel level yes. You just create a custom sensor on one of the analogue channels. Depending on the sensor you use you may need to change the sampling frequency in the AIM software.