again, I have to come back to the question, which gateway process are you using?
For sage pay it will be one set of instructions, for paypal standard it will be a different set of instruction and for Express checkout, it will be yet another set of instructions due to the differences in the ways these checkout services work
There are two differant types of checkout methods:
Local Checkout - this is where the user enters payment information on your site
Remote - This is where the user is directed to the gateway to enter payment information.
Payments Standard and Sage Pay Form are both Remote services, the draw back to a remote service, is that you need to rely on the gateway for things like sending the receipt email
using a local checkout service (PayPal Payments Pro or Sage Pay Server) The wizard will configure Universal Email for sending the receipt. I understand the draw of using a remote system (Cost) but the development for using a remote system is much more complex.
I always recommend using a Local Checkout method, it may cost a little more, but you get what you pay for.
It is _possible_ to have email receipts using universal email with the remote payment services, but it is by no means simple.