Did Squeenix really design their servers so that people can create more characters for a server than the server can handle at once? I keep getting this error. Does it really mean that the world is full, and I have to wait until someone logs off until I can log in?

I hope its just an error and not the truth, because that is a terrible system. There are server limits for a reason, so your playerbase isn't stuck unable to play because there isn't a server restriction on the amount of accounts on one server.

If they are going this route, then at least go with Runescape's method - each server can hold a set amount of people, and if one server is full, just log into another one. Either that, or they need to make restrictions on the amount of characters that can be on a server - when the server population is full, no more characters can be created on it.

It doesn't help that the game doesn't have a logout timer for inactive players, or even a login queue, you just have to spam logging in until it works.