If you are building a site that has the potential for information that will never age and remain useful for your audience, you have the opportunity to create what is known as evergreen content. It's important to carry out extensive keyword research before planning any evergreen content for a site like this, as your site could hugely benefit from the proper usage of keywords within such content.
Yes and no. Affiliate marketing can generate passive income, but the passive side of the income usually only follows putting in a few years of hard work to generate the brand and audience you'll need to begin generating those passive sales. I have multiple sites earning passive income, but each of those sites took a lot of front end work to build up to that point. And not every site gets to the point of passive income. Some sites require continual maintenance though the revenue they generate can also allow you to pay for that maintenance to be done vs. you needing to do it yourself.
If you have built up an email list, you could also promote your affiliate offers via email promotions. Just make sure you build up a relationship with your audience first instead of going for the hard sell straightaway. The emails you send out must contain your affiliate links to products so when your audience click through. the sale is attributed to you.
Clickbank is a market platform for vendors (product creators) to sell their digital products. Such products could range from ebooks, downloadable resources/programs or online membership sites. On the flip side, it’s also a place that widely attracts affiliate marketers to help these creators sell their products, essentially giving them a source of free publicity and advertising in exchange for a commission fee on every sale.