Consider your expertise. If you take the time to reflect on your experiences, you will realize that you have more knowledge about which to write than you might think. Begin by listing three assets that define you, such as your profession, a special hobby or a personality trait. Next, list three things that inspire you, such as religion, education or charity. Finally, list three of your dreams, such as getting married, traveling or spending more time with your children. These three lists should give you many ideas of topics about which you can write.
I do have a question, though, you state that longer articles are better (which I understand). I've found a niche that has a few keywords with very high CPC (no real affiliation program can be used though), with a few thousand searches a month. For each keyword I could probably 500 words on each keyword. Should I do this, or should I compile them into one big article? They keywords can be linked to each other, for example, "how to start running", "basics of running" etc. (Those obviously aren't the keywords, and more can be written on those). What would you recommend?
Now as to your comment on traffic it is true, traffic is important. But the truth is, acquiring traffic is easier than converting it. Plus we have many posts dedicated to traffic generation on this blog. Simply check this post, this post or this post. But must importantly, the reason why people struggle with traffic is that they try to promote a sales page or a heavily biased piece of content. Nobody wants to share that, nobody wants to link to that, and as a result you don't get traffic and blame your lack of success on traffic (like you did in your comment above).
Since you’re essentially a freelancer, you get ultimate independence in setting your own goals, redirecting your path when you feel so inclined, choosing the products that interest you, and even determining your own hours. This convenience means you can diversify your portfolio if you like or focus solely on simple and straightforward campaigns. You’ll also be free from company restrictions and regulations as well as ill-performing teams.