How do I know if what I am doing is 'working' with my article marketing?

Yup I have been doing that.

The most clicks (unsurprisingly I'd think) so far have come form the keyword optimized article.

CTR is about 9%.

The metrics you should track are pretty much dependent on your sales model. From what you've posted, I'm guessing your desired flow is something like this:

Article --> Landing Page --> Vendor Sales Page --> Vendor Order Page --> CB payment page

Now, just look at the steps someone would be required to take for that to happen.

1. Someone has to see/read the article, so you track the number of views.

2. They have to decide to visit your landing page, so you track the number of clicks.

3. They have to read your landing page, so you track time on page.

4. They have to see/read the vendor sales page, so you track the number of hops.

5. They have to click the order button, so you track the number of order form impressions.

6. They have to pay for the item, so you track sales.

Much of your room for improvement will come in the ratios between some of these numbers.

One is the CTR, or click-through ratio. 100% is perfect, and you won't see 100%. You lay down a baseline, then work on improving the ratio rather than shooting for some 'normal' value you read on a forum.

Once visitors get to your site, they need to move on to the vendor's page, so you look at the ratio of page views to hops, another CTR.

Once they're on the vendor's page, you really can't do much to influence the results, but you still want to track them to see if you have better opportunities elsewhere.

For example, if you were doing a good job getting article views, moving them to your landing page and then to the vendor's page, but the vendor was doing a lousy job of converting your hops to sales, it would indicate that (for you, at least) another product might be a better option to promote.

I know it's nice to have some kind of average number to compare with while you create your own, but it's also dangerous. An average is created by essentially using the very good and the very bad to cancel each other out until you arrive somewhere in the middle. If your project has the potential to be one of the very good ones, you don't want to stop pushing just because you hit a "typical" value...

Ah, yes, the powerful list! But, once you get your list, how are you going to 'take care of it'?

You can check you hop stats within CB to see how many hops you've got (Account homepage -> Reporting -> Analytics).

You can also use some link tracking/redirect software like Ghost URL or Easy Redirect Script. They also track links clicked on your site.

You visitors and Google will like that you also provide value to people, and not just try to sell them stuff. It sounds like a semi-solid plan... Though in information markets I would definitely build a list to get better conversions, and get more value out of each visitor in the long run. It's like recycling your traffic.