There will be a 24 hour "open house" period where anyone who is 18+ and has a MetaMask wallet can join to test out the game and see what is possible. This will also be a stress test, of sorts; it'll allow us to see how the game copes with more users.
Even if you don't own a Habbo Avatar or a room, you'll still get access to the Habbo X furni catalogue. However you'll only be able to place it in your avatar's demo room, which is the smallest room possible and is not an NFT.