Under what circumstances do items count against your hand limit? It's my understanding that a big rock or something counts against your hand limit until you throw it, at which point it's available to be picked up by anyone. But how does that jive with things like tacks which are meant to be dropped on the ground immediately - are you still maintaining the spell even when the item is just laying there?

But then once someone picks it up, does it count as being maintained by them?

Also, under what circumstances can you dispel an item spell? Only if you're holding the item? Only if you're the original caster?

With items that are dropped, I place the token on the board and then immediately after place the item card next to the board too. Because you have lost ownership and it has dropped, it lands in "neutral" territory for anyone to pick up and use. When a wizard picks up the item token, he gains the respective item card. That's how we play and I'm not sure how close the rules relate or identify what in fact should be done procedurally.

I play this way too. The nuance is the following, play an item is a mundane action and maintain a spell is a magical action. When you play a item card it is permanent and you can´t decide discard it (you can drop it) and if you die the item remain. When you cast a spell you have absolutely control of it, you can decide when stop it and if you die the spell is discarted and the effect ends.