Adding onto existing campaigns

I have GW prophecies and EoTN and I'm thinking of buying Nightfall.
If I register Nightfall on my existing account will I get extra character slots and if so how many?

You add the keys you get from the NF box to your account you have already :
)

i believe you get 2 more slots if you attach it to your existing account

I believe that if you guy NF it will give you two (2) more slots.

You get 4 for the initial campaign on your account, and 2 more for each added campaign to the account. EN doesn't add any though. Also, make sure you don't make a new account with NF, seen it happen with friends too many times.

wouldnt gw disallow someone from creating an account with an email login that already exists?

and y would they use a different email login than the one they're already usin?