The PF was my 1st ET device.  I still use it on a backup ‘board.  Great pedal.

1).  Yes, and no.  LEARN is a Performance Parameter, locked to one or the other algorithm / Preset.  So, you can assign two separate HotSwitches to LEARN, one for each algo.

But your mult scheme might still work, plugged into the EXP/CTL jacks 1 & 2.  Haven’t tried that, but in theory, you would reassign the LEARNs to SW 1 & SW4, from one Aux switch.  I’ll try that out later on.

Presets in parallel, of course.  In Series, you’ll get a real mess trying to LEARN the LEARN.

2).  You can reassign two of the Quick Knobs to display Key (momentarily upon LEARN).  But if the H90 is on the floor, you’ll have to be fast with your binoculars.

You can bring that back up again (momentarily) with a press on the assigned Quick Knob(s).

3).  While the H90 can receive on multiple channels in Omni, Program Changes will affect the entire Program.  You can’t target reloading one or the other Preset half.

In this respect, think of your two PFs as 2 separate Global devices, and the H90 as a single Global device, made up of two distinct parts.