Emails can be managed via the menu System->Emails in the Business edition. You will be able to activate/deactivate them there as well as modify them.
Yes, an account is created for them. When they click on the confirmation link in the email, they will be logged in automatically on the checkout and they will be able to continue the checkout process.
Then, when they want to order again, they will be able to login with their username/password and their address will already be there, so less work for them.