I was just wondering how close to 100% I need to be in order to fulfill that category. Would it be every single stud and brick on every level? Or every collectible?

It's getting 100% on the pause screen. I think that just means getting every canister and golding everything? But it might include the bonus levels you have to get from the shop as well. We haven't finished routing it yet. If you have discord, we can talk about it there: https://discord.gg/WXmTptY

I'm fairly sure 100% means getting all collectibles (silver and gold canisters), getting all gold medals, and unlocking all items (according to a "guide" I looked at, hints don't count toward 100%). I do not know if the piraka items must be built/used in the playground or if they must simply be purchased. From the same guide, it would seem that the Bonus Levels must simply be purchased but not played since they do not have a medal associated with them, but this is unstated.

I can confirm that hints do have to be purchased, and the bonus levels have to have Gold Completion status. From my looking into it, the piraka playground toys have to be purchased, but it doesn't matter if you build and activate them. The ruleset for the category has also just been updated, so if you are still interested, take a look at it.