Will using the 5v external ?Amps supply the requirements for the shield?
Yes, all power from external 5v supplies necessary voltages for the mpcie card
How much current is @ 3v3 out pin ?
Not connected by observation , only in schematic.
Are all ground pins on the same thermal plane?
Hardware specification 1.4 for EC25 850ma for LTE, possibly 2A supply is adequate.