2) Exactly what squish clearance I should be aiming for?
I've heard that  1.397mm (0.055") is the ideal.

I've heard it was .050 but that can be fine tuned to a degree with Base gaskets.  The Cometic AFMs squish down to from original numbers to around .012 / .018 / .032

Adjusting with base gaskets will alter your port timing also, I imagine it gets complicated and I am not qualified to give advice so somebody else would be best to give you information.