I just wanted to say that @jurky3fo imparted some high level stuff - don't let it blow right over your head.
If you do anything that has more than just a single or a few product offers, you want to be paying attention.
By the way, it also helps with small websites if you understand how to tweak it the right way.
Silo architecture is the secret sauce of SEO. Matt Cutts is on video saying that silo architecture works. If you aren't siloing your content you are killing your website's ranking power. Once you understand how to sculpt link juice (without nofollow), things get real easy. I recently watched a very competitive keyword jump from #176 to #12 with Zero backlinks by adding 12 pages of content into its silo. It's magic.
Google is always looking for nodes of authority. When it finds a tightly themed silo with 5 or more high quality supporting articles, it puts the parent page on steroids. For any keyword, there seems to be a magic number for supporting articles that catapults the parent page to the first page. You can absolutely, positively get pages ranked with far, far fewer backlinks. The best part is that it's update proof. How often do you see an authority site get hammered? What's even better is that you can get other keywords ranked by accident! With the authority site I am currently working on, I had many "holy shit" moments when highly desirable, competitive keywords that I wasn't directly targeting got ranked in the top 5 out of the blue. For long term success, the goal is to establish your site as an authority. When you hit critical mass, you can get new keywords ranked very easily simply by creating a new silo with a few supporting pages. Your site becomes a ranking machine that powers itself.
For on-page, I use SEO Pressor, and a minimum of 500 words. I look at it as more of a check to make sure I've got all the bases covered. Samx's post is spot on for onpage.
Content these days is cheap. My site is in the Information Technology vertical, and I get awesome 500 word articles that look like someone in my company wrote them for $15.
GSA is an awesome product, and tiered link building is a great strategy. I use it. But... If you are trying to build a website on link spam alone, it is the lazy mans approach, and it is not going to last. When it comes to content, give Google what it wants, and what they want is high quality, tightly themed, siloed content with solid on-page optimization. No tricks. Build a solid foundation, and use Link building as a supplement, not a strategy. Feed the beast. Keep pumping quality content into your silos.