What is the official Collect 1 Million Items Roblox link?
The experience page is https://www.roblox.com/games/133363783004873/ and its creator field reads Rsix Studio, the same group this page lists. Any page credited to another creator is a copy.
Is there an official Collect 1 Million Items Discord?
Not that the developers publish. Neither the experience nor the Rsix Studio group links to a server, so a server claiming to be the game's official Discord is not the developer's.
Is there an official Collect 1 Million Items Trello or wiki?
No. The checked sources list neither a Trello board nor a developer-run wiki, and this site does not publish a substitute for one it cannot attribute.
Does joining the Rsix Studio group do anything in game?
Yes. Joining adds a permanent +1 Luck to your account, which is why it is worth doing before you start rolling for abilities.