Arre: The Campaign

The general advancement plan is this-

PC level 4- Base item would be +1 (if applicable) with some kind of spell like ability of 3rd level tops, or maybe a virtual feat or class ability available at 3rd level.

PC level 9- The first bump would be +2, level 4-6 spell, VF, 7th level class ability.

PC level 13- Next bump +3, 7-9 spell (with adjustments like Amadeus’ ear trumpets 1 minute Premonition), +2 ability score bump while in use, VF.

PC level 16- Last bump is losing attunement.

All PC levels are subject to change.

Of course unique features could be a thing at any time.

The right to tweeze abilities during the game is reserved.

So for instance, the Helm of the Harbinger would progress as +1 to ability checks and allow Devil's sight to 120'
Then it could give +2 to checks and allow telekinesis once per LR,
And finally +3 to ability checks and cast Rarys Telepathic Bond once per LR ( If that's still a spell); otherwise I think it should probably be Death Ward.
Finally, the bearer gets his slot back at 16th