You should be working on your whole site. Now that being said, some of you might find that idea overwhelming so just take it in small steps, work on optimizing and link building a page at a time.
When you are link building, you don't have to get links to your home page, you can build links to an inner page when the place you are submitting your link is appropriate. Some places (like directories and resources pages) might only allow root domain links (linking to your domain name) so also look for opportunities where inner page links are allowed.
You might also want to look at Google Product search. There's a discussion here at V7N here:
Are You Using Google Product Search?