A word of warning, get an after market fuel pressure regulator if you are going with the 255, then bypass or drill out the j-tube. Also when you were saying about the pump priming itself, the mk3 does NOT prime itself like a normal car. The cranking signal turns on the fuel pump then the maf/afm signal takes over to keep the fuel pump running, its strange but true. So turning the key on and listening for the pump will do you no good. Also you should check to see if the pump was bad, or if it was the wiring or fuel pump relay or fuel pump resistor, and if you are going to be doing the pump anyways look up the fuel pump rewire and resistor bypass.
I has serious problems with my car after putting the 255 in it, at 75% throttle it would blow thick black smoke and I checked and saw I was around 70psi on the lines, I dont know if it was from the j tube or the fpr or both but put the after market fpr and bypassed the jtube and no problem. Also with the walbro unit I got it does not seem to have a backflow preventer or it was not working properly so fuel pressure drops back into tank so it takes a little bit of extra time to start the car now.