Suspending many lightweight acoustic panels from a plaster ceiling
A couple ideas...

Go with your magnet idea, using either the moly buttons or magnetic sheet bonded to the back.
Use simple silver screws in the ceiling. Almost any ferrous screw will work, and you don't need toggle bolts. Either you'll hit lath, the plaster itself will hold, or you'll add a slim plastic plug anchor for troublesome cases.
Insertion depth gives you leveling adjustment. I don't think swivel adjustment is needed due to the very shallow angles.

Otherwise, you could use leveling feet...

Commonly available furniture feet with ball sockets give you angle adjustment.
Depth of insertion gives you level adjustment.
You'd need to use plastic inserts to accommodate the machine threads for some holes. Those in wood probably wouldn't need anchors.
Therefore, you'll want the smallest diameter shafts you can find.
I'm not sure how you'd attach the panels to these. Maybe magnets. Maybe double-stick foam tape.

However...
I really think that some small foam blocks and panel adhesive are what I'd do...

Cut 1&quot; or 1-1/2&quot; thick sheets into hexagons somewhat smaller than your panels. I think 2&quot; is too much, personally--I'd want them a bit closer to the ceiling and I'd want the mounting hardware totally hidden.
Bond them with panel adhesive, which has quick grab. Use the press-remove-press technique for instant hold.
While things are soft, make leveling adjustments. You should be able to stretch the adhesive for some time after mounting.