SEO for a Spanish version of my site

I am almost ready to publish a Spanish translation of my site. This will be a page for page duplicate of existing english pages. I plan to put a link to the spanish "home" page in the header template on the english side and back to english on the spanish side.

The target market is spanish speakers in the USA who will probably have to shop for the products I describe (home improvement items) in english oriented stores. For that reason I plan to put a link in the content part of every page that opens the other language page in a new window.

If, for example, a visitor is reading a spanish page about how to caulk prior to painting they can click this link to see the identical content in english. This will help them be sure they buy caulk which is paintable :)

I am assuming Google will be able to figure out that some pages are spanish and serve appropriate ads.

Am I missing anything or doing something I'll regret?