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.
Once you have signed up, you will receive your Associate ID ending with “-21”. You must keep your Associate ID safe as it will allow you to track your links. As soon as you receive your Associate ID and your application is approved, you can start tracking your links to Amazon and earning advertising fees. And that’s it: you are now an affiliate of Amazon!

One thing I do is have websites that are set up in lower competition niches where the items typically aren’t as expensive and where it’s easier to sell these products in larger quantities ($50 or less). Then I have other niche sites that sell more expensive products at much higher prices ($XXX – $X,XXX) that are sold less frequently. So this way I get to use the increased quantity of sales from these lower priced product websites to help me get up into higher payout brackets so instead of making 6% on that high end item I’ll get 8% instead.
Small-scale bloggers like Robey won’t be the only ones hit by the rate changes. Publications like The Wirecutter have built thriving businesses entirely on affiliate payments, which are made by vendors like Amazon whenever a referred customer buys a product. Though a number of companies offer similar programs, Amazon’s affiliate system is the most lucrative, and auto-tagged product links have become a significant part of many online businesses’ revenue. (That includes The Verge, which auto-generates affiliate links in some cases.) Though the relationship can be lucrative, it’s also entirely subject to Amazon’s discretion — and as Robey and others are learning, it can often change with little to no warning.
For Mike, who got married and became a dad during his almost two decades at Amazon, ownership isn't just about getting work done; it's about leaving work behind and recharging with family. "I manage my schedule really aggressively," he says. "If you let your calendar get filled up with non-essential stuff, you're not owning your career, and you're not owning your path. You can be scrappy. You can be entrepreneurial. You don't have to give up your personal life."