fuel pump should be fine.I have a 89 Pulsar and a 89 Sentra, I will most likely be doing the MPFI on the Pulsar since it is not my Daily driver. The only difference is the body shape between the two, and the pulsar is shorter than the 4 door Sentra. The engine compartment and components are the same though.
On the GA16DE I think you are right with the OBDII computer, so I will get one from a pre 1995.
On the injectors I am 90% sure that the MPFI GA16DE is like the majority of the other MPFI systems I have delt with, it fires all 4 injectors every time for every cylinder, so if I run them all in paralell from the GA16I computer it should be ok. My greatest concern is fuel pump/pressure, and the coolant passages in the intake.