Being in Australia, I’m not required to do anything by the law (although I hear talk that there may be changes around this). I don’t disclose every single Amazon link on my photography blog in a direct way but do I have a disclaimer/disclosure page on the blog. When I’m doing a ‘best seller list’ always include a disclaimer on those posts as the whole page is filled with affiliate links. I have also written numerous times on DPS about how the links to Amazon earn us money and help the site to keep growing and be free.
The ego is the driver making the decisions. It decides between the devil (the id) and the angel (the super-ego) on either shoulder (yes, all those cartoons you've ever seen are partly true). We have voices in our mind, and it's up to the ego to decide which one to fulfill. Its goal is to satisfy the id in some way while also attending to the super-ego.
One great way to get ideas for related products to promote is to look at the stats/reports that Amazon gives you to see which products readers are buying. After a while you’ll start to notice that they’re not only buying the products you directly promote but other products as well. Some will be completely irrelevant to your niche – but many times trends will emerge that could signal other products that it might be worth promoting.
Analytics are limited. Unlike with conversions made directly on your WordPress site, you’ll be limited in terms of what you can learn about the people making purchases through your affiliate links. While Amazon does provide you with details about clicks and sales, you won’t get deep insights into who the consumer was and what they did on your site before they got to that point that you would with Google Analytics.