Tom, from everything I'm seeing, you can't import epub (or any other) format books to "Google Play Books" (yes, that's a dumb name). My guess is that you'll need an alternative app for this. I'm seeing some positive stuff about Cool Reader.

I hope to join the Nexus 7 owners sometime

*edit*

ps- you should be able to store the books wherever you like and point the app to where they are. Some apps will automatically scan for supported file types, others will ask you to point them to your preferred folder, others will insist on a single set location of their own.