Don't sweat it*, IF set up properly, these 2 IDs (the one from your ISP and the one ending in iCloud are linked.)
But to be Safe:
A) First, check your current iPad if iCloud lists the account with the @iCloud.com, Set up your iCloud Account on the new iPad using that.
Then, after you've gone through initial settings:
B) Open iTunes, look under "Store" menu to determine you "Store ID", it'll read "View account (whoever@comcast .com)" or something else.
ALTERNATELY on your old iPad select Settings>iTunes and App Store (your store ID is at the top)
either way, enter this one under Settings > iTunes and App Store" on your new iPad
That's it.
*no matter where you buy your music, they all link to an email address (which can be an issue, if you ever start getting spammed.) I'm so paranoid I burn all my music as an audio CDs, so there's just no way to loose it completely due to DRM issues.
Good Luck. I'm very jealous, just can't rationalize buying the Air, since I just got an iPad 4 last year.