This is what I would do in your situation hope it helps
1: I would use create a product page (or shop) for the main product and add the related items below your main product on the same product page, saying something like
If you like …(main product)…. you might also like: and list your other products here
Just like amazon would promote related books and products really
Amazon does offer a lot of affiliate tools, i know you can get code to show specific products and list the ones you want to list on your product page, I’m not sure about the page you’re talking about might be a specific amazon wp theme. Hopefully someone who is an active amazon affiliate will know
2: I would keep it seperate too, like you said the mindsets are so different (buying v make money) I would segment the email list first to get people who are open to make money on a new list and promote the biz opp to them..
Hopefully more people will reply!