Hi cap217
1) no KPA do not feed Phantom power so You need another device to use those kind of Mics.
2) You need a mixer
3) Use them like You normally use them in Your Signal chain, just remember to give back to KPA a Return Signal.
4) You can try with and without, then compare the results and choose what You prefer.
5) this actually depends how the Amp You're going to profile is made, what kind of Output it has.
Consider that KPA allow You to get a Profile only of the preamp of an amp, (usually called here DI Profiles) IF the amp has a dedicated output for that (i.e. the Send Output of the FxLoop in some models, or the so called D.I. Output in some other amps)
it depends by the amps itself, how the circuit has been designed.
And KPA also Allow You, Using some other external and Appropiate devices, to get the signal that comes out from the Speaker Output of Your Amp ( here called DA Profiles or, the first step for a Merged Profile)
butlike You said, if You're going to Use profiles through a mesa power amp and mesa cab you will have more faithfull results with a DI profile, not a DA ones.