You should be able to use the same gateway information on both sites.
If both sites are on the same server, you might be able to share the database. The store name and email will be the same for both, but you'll share all the product info and stock. Just remember a change made on one site may effect the other site. You'll have to use the same custom template name, but you can change the information in the custom files to make the sites look different.
If you're going to set up a separate database, you don't have to think about that stuff.




