1. My idea was that yeah if you submit an item, it gets taken from the inventory, and yeah technically in that case, it'd lowkey be a bit of extra storage heh

2. If a collection asked for something like 5% rarity or lower deco then yeah, 10 of the same rare deco such as grand pianos should, ideally, work! Well, unless the collection requirements specify that they need to be unique items

3. I think, depends a lot on how the code would be made to work by whoever codes it. It'd definitely be cool if for, say 15 stone eggs collection, you could submit 60 stone eggs at once and get 4x the rewards instantly, but yeah I can't really make such predictions for if this feature ever does become a thing