There are several small fuel flow sensors around, although most inexpensive ones I've seen are for water use and have standard 1/2" (12.7mm) fittings. I am sure these will work though, but you would have to check that it is suitable for Jet fuel.
Check this one, although it is for higher flow rates.http://www.seeedstudio.com/wiki/index.php?title=G1/2_Water_Flow_sensor
There may be some that have a smaller range.
As for the other issue about measuring the fuel quantity, I have been doing several experiments with capacitive sensors, and the real simple way to see how much fuel you have is to place a series of parallel conductive strips down the sides of the tank, (front, back and sides to get an average when not in level flight) and measure the capacitance of the strips. I used self-adhesive aluminium tape. This changes quite a lot from full to empty, but they are still in the region of only a few nanofarrads. A lot of processors have CapTouch interfaces these days and this makes it easy get readings. I haven't yet seen anything on CapTouch on the Arduino processors, but you could use a 3rd party micro to do this.
My first experiments involved using a LM555N timer IC and the capacitive fuel sensor as the timing capacitor in the circuit. I had to use the right resistor and capacitor values to get a reasonable range in frequency. Then you simply use one of the frequency counter libraries available for the Arduino and calibrate the readings. You will have to use the normal fuel you use to calibrate, as using water or some other fuel gives different readings. The dielectric constant of Jet-A1 is different to other liquids, like methanol (for piston powered models) or water.