A) As long as you like Willamette, you should be fine adding it to your Pale Ale recipe
B) I'd mash really low as an insurance policy with that much Crystal malt.
C) How much is a "crap load" of Cascade and Willamette? If it were me, I'd leave the hop schedule as-is, but add an ounce of Willamette to the Cascade at flameout. Then dry hop with an ounce each of Cascade and Willamette.