Can I use one of your cool pre-designed online templates on the Design Your Own web page?

Yes!  You can pull in any template background on the Design Your Own feature by using the Background tool.  You'll hover over that, then go to Add Background Artwork.  This will bring up a window where you can search for your template.  You can search by theme, such as "soccer" or "BBQ", or you can search by color, if you don't know what the template is called.  Add "raffle" to your search if you want the design to have lines on the stub for your customers to enter their contact info.