First question: Can I set up the reverb switch per patch to control comp/amp/loop/verb?  Or am I limited just to turning reverb on/off with this switch?

Just 'verb

Second question: Can I use any footswitch in the same way I use the "TONE 2 / HOLD FOR DUAL" switch on the X3L?

You can configure the FX Loop switch to control Dual tone instead, and yes, then it works exactly like the "TONE 2 / HOLD FOR DUAL" switch on the X3L