I would compare the polyphonic tracking side-by-side first, if possible, between the Boss & H90 / Polyphony algorithm. Both are very good, but it boils down to the ear of the beholder.
No, the H90 won’t do the ‘lowest note’ feature. If ‘each function simultaneously’ refers to the octave selections, then yes. Of course, it won’t do the Boss-specific Vintage Mode.
The H90 will clock to a drum machine, system-wide. You can run Polyphony (or another pitch-shifting Preset) in series or parallel with a Looper Preset in a single Program.