Had to put this "synchronize_data := false" on the create_subscription call. Weird that there seem to be redundant parameters for this; one on the replication set add and one on the create subscription. Maybe I'm not quite understanding the usage on those or something. If anyone knows the difference, I'd be interested to hear.
Yes. When you add a subscription with sync = true, then all tables in the replication set(s) will be synced. But suppose you want to add a table later to the replication set. Sync = true will sync only that one table. So the latter is more granular.