So far I've been paying the monthly entry-level subscription, which gives you eight characters total and they have to be on different worlds, and I'm at the point of contemplating whether to upgrade it to get the higher number of character slots.

Mainly I would like to know what happens if you go back down to the limited sub again after you've added extra characters to your account. Presumably some get shut off, but which ones are you left with? Earliest created, most recently used, or some other rule?

Also, can I upgrade in the middle of the month or would it not take effect until the next time I am billed?