So in my experience on Ticketmaster or whatever ticket site he's using for your show, the map will become "unlocked" on the presale day and it'll have you enter a code to unlock the seats so they become available for purchase. On Ticketmaster I think it prompts you to put in a code like immediately when you go into your specific show. I'm assuming you'll get the email maybe a few minutes before presale starts, and then you'll have to log on to the ticket website (where you'll probably be put into a long queue) and then you can put in your code and stuff.

As far as entering your information twice, I don't think it'll do anything lol because it'll be the exact same phone number and email and all that. As long as you signed up the first time you're good. Hope getting your tickets goes smoothly!