The Amazon Associates Program is one of the largest affiliate networks in the world that helps content creators, publishers, and website owners monetize their traffic. With millions of products to choose from on Amazon.com, Amazon Associates use easy link-building tools to direct their readers to products and earn from qualifying purchases. Not only do Associates earn commission on products they refer traffic to, they may also earn on other products their readers may purchase on Amazon. As an associate, you'll have full access to a suite of reporting tools to help you learn what resonates best with your readers.
You can sign up as an Amazon associate straight away without a site. As long as you have the URL and it belongs to you. They won’t approve your site until you have made your first commission. So what I would do is get the site built and add all the content that you need. Make sure its finished. Then sign up to the Amazon associates, add in your aff codes to your review pages and then you just wait for your first sale. Make sure you read the amazon T&Cs so your site is compliant. If it isn’t then they will not approve your site.
I found Clickbank via another website and I found an offer for a free tactical flashlight. I should not have ordered the "free" flashlight since there was a shipping charge and a hidden membership charge. The membership is not disclosed and I did not agree to one. I canceled the membership and I unsubscribed to the website that guided me to Clickbank. I will ensure in the future that I do not fall into this trap again.