So you wired 12v through a switch to the pump and it turned on.
That eliminates any ground issues from the pump . Still doesn't eliminate the AFM or the ECU. Check for a ground signal coming from the ECU. Get the ECU pinout and look for the fuel pump signal. When the ECU is powered up just before starting the car, you should get a short to ground on that wire. That will ground the relay and send power to the pump. If not, you have a problem with the ECU. If you do have ground, then check the connection to the relay. That connection should also get ground when the ECU is powered up. If it doesn't, then you have a bad connection from the ECU to the pump relay.
Your gonna get tired of that pump switch after awhile.
Just think, if you get it running right, you'll have bragging rights.
My pressure is released when the engine is turned off after several minutes also. I think that is normal.