Yeah looks like the 12" is 150W RMS so you definitely won't need the mono.

Since the PDX runs 100W RMS per channel @ both 2 and 4 ohms then you simply add the two channels together to get 200W RMS for a bridged channel. (it usually isn't that simple a calculation)

Keep in mind that Alpine amps consistently output more power than their ratings would suggest so you'd be looking at well over 200W RMS going into the sub so don't up the gain any more than two thirds or so!