First make a group above the background layer.  Do all you work in here.

I put all the CS parts apart from the background in to a group on it's own and then I lock it to stop it being mistakenly edited.

Now the best way is just as your said.  Do what will be the left hand side first.  Then copy it all and move it over to the other side, of course, fliping and reversing as needed.

Logo's that go over sections can be masked to hide the bits you don't want to show.

All the tools I have mentioned can be google's for simple instructions on how to use them.

Logos and that can be found on sites like this one.

http://www.brandsoftheworld.com/

I use this as a good source of reference for my work.

Just ask if you need more info.

Dave