I think that the account details on the MogStation should be able to tell you how many characters you are allowed to create (per server). But, from what I remember during the transition period to ARR, the game has 3 types of subscriptions: Entry, Standard and Legacy.

With the Entry subscription, you were allowed to create up to 8 characters (1 per server). With the other 2 subscriptions, you were allowed to make up to 40 characters (limited to 8 characters per server).

But, like I said earlier, the MogStation should be able to tell you.