I'd love to make a game for others to play at my island. Of course, there is the permissions block that does not allow any player to actually click a button/place blocks etc, so I need to know if I can use pressure plates with users or items users drop.

Firstly, can a user's item, if they drop it, trigger a fine pressure plate to manipulate a piston? I HOPE THE ANSWER IS YES. If this is so, a user can fling something cheap (a watermelon slice, stick or snowball) onto an appropriate pressure plate to move pistons.

If it doesnt DIRECTLY stimulate it, can a thrown object get put into a piston, and then jetted out with a dispenser automatically onto a pressure plate, so that it might trigger a piston?

FINALLY- can a user just stand on a plate to trigger a piston, even though they dont have island permissions? I am guessing I'll need thrown objects, but this would be a nice way to avoid all of it.

If I need throw-able objects, is it possible to allow one single chest to be open to the public? I could fill it with snowballs or sticks for users to play with, and they could get subsequently sucked up by droppers and re-deposited into the trunk... It sounds complicated though. :/

To give you an idea of what I need, the game would be a simple puzzle game. You'd have a plain of scrambled blocks, and each block would slide at the command of a piston. Users would be challenged to make a certain shape (square, pyramid, smily face, whatever) out of the scrambled blocks by sliding them around with pistons. I think this would be a really fun thing to add to the server, and the pressure plate is the only way to make the game available to the public while keeping the rest of my island private.

So are the pressure plates a viable way to do this, or do I need hoppers? I have 0 iron btw... lol. It will be a long saga, but hopefully worth it!!