I looked up the Subterfuge global leaderboards and I am not listed, so my question is at what point will I get placed in it?
I just joined (Completed 1 casual game with 1 gold medal) and am on my second game.
Or is the leaderboard only for L2, as I see that everyone on it has at least 1 ranked game? That would make more sense to me, as there are fewer L2s than free to plays.

The leader board goes by rating, so only L2 players who can play in rated games would be listed I think.

You need L2 In order to join ranked games, ranked games are how you gain rank, and I'm pretty sure you won't be listed until you gain/loss some rank (or else the leaderboards would have over 10,000 people listed as 1200 [starting] rank.