How can I find out when my account will expire alter a pay period? I don't remember when I last paid for the monthly subscription. I can check when I last signed up, but not the last billing activity date.

I am planning to eventually go for the 24 month period when I have the time to play this game again, but I didn't want to have to start over from scratch!

You won't have to start over from scratch. Even an account that has been unpaid for over a year (and probably much longer) will still have everything it had before.

The Billing Options link to the left will tell you when you are paid up until.

Other questions can be handled by emailing:
billing at guildsoftware dot com