Useful points Grab.
I did suggest foam covers for the mics to stop wind noise. IMHO these will be more use than the stockings used in studios.
As I suggested, using a separate power amp for the foldback will leave the FoH seeing 4 ohms, and producing 375WPC. Sodded if I can see hos to do it from the manual, though!
I'm almost sure some of teh Phonics gear does run down to 2 ohms. Allegedly not this one, although I see it will go down to 4 ohms bridged, but still only a mono 750 watts. Good trick that! Worth trying cautiously even if it doesn't. It has an internal limiter and I think a thermal trip. I have a huge Audiohead that is supposed to be 3kw into 8 Ohms bridged, and it seems fine into 4 ohms bridged, although it tends to run woofers off their endstops!
Out of doors, feedback is probably unlikely, if the speaker situation is halfway sensible. The graphic on the Phonics is probably too coarse to mae a lot of difference and still have the voices sounding human.