lol
bottoms up !

magnet wise I've got quite a few.
Duct wise, yep a bit more width and depth wouldn't hurt the airflow :-)
No clue if the turbo nozzles work or not. definitely no air coming out the holes, but even a small bit of tissue doesn't stick, which you assume it would if there were a vacumn being generated.

As far as hot glue guns go - I'm not a big fan. Rather use epoxy putty or uhu all purpose glue. Particularly for something as smooth as a ball bearing.
For the arms I'd probably go with the uhu glue. the magnet would hold the ball tight to the tube while the glue set, which is pretty quick.
Dunno what solvent they use but it even eats pet-g :-)

Dogs back - gotta go wield a towel :-)