Quartney, you are absolutely correct, but whether or not you need to glue down the bottle caps depends on what you want to do. For my bar, I wanted to grout between the caps to add a black background for contrast. I glued the caps down to prevent them from moving around as I applied the grout.
No matter how you want to make your bar top, it's a good idea to make a prototype or two to get familiar with how the epoxy works and to work all the kinks out of the process. For example, I found that if I stirred the epoxy too long, it accumulated so many tiny bubbles that it wound up looking cloudy as seen in this picture.
I used cheap wooden trays from the craft supply store. You can see some of them here: