The PIC will operate with as little as 2.0 VDC.
Fine (get the differential model). Although you might want to consider a mechanical buffer (diaphragm) of some sort to keep moisture away from the pressure sensor face.
Not necessary. The PIC18F46J50 has built-in (multiplexed) A/D converters. You will, however, have to use a resistive voltage divider network to scale the output of the MPXV7025 to, for instance, a 0 - 3.0VDC range. Not a big deal.
Fine. That's covered.
The PIC18F46J50 also has a USD 2.0 interface, which I would prefer using. The RS-232 and RS-485 serial comms are more difficult to work with.
I'm assuming you have access to a PIC programmer.
Just some thoughts.