People looking for books online likely have more disposable income than the average population. So I would say ad revenue will probably look pretty good but this is just a guess. Sometimes this can be surprising for different niches. For example, you might not think recipe websites make much money but in fact they often make $30 per 1000 visitors (on ads alone) due to their audience profile. I got turned down offering $140k for a recipe website a few months ago. They were making around $3k per month.
As far as affiliate revenue, they are very likely to be making a purchase soon if they are looking at book reviews so if you can get them to click your Amazon affiliate link there will be fairly high conversion. The revenue per purchase probably is quite low due to the price and margins on a physical book (although I wonder what it looks like for Kindle books) but with enough traffic you can absolutely make it work. I can think of some interesting ways to get a lot of traffic with Pinterest as well in this niche.
This is a numbers game. Keep your costs low and your time involvement low and even if it is only making $2k/month that is good enough because you can have several sites at the same time.
Btw as far as needing a ton of traffic to make money well sometimes that is true to an extent. Recently I was looking at a website that was the most popular user-created website for a specific mobile game. It is generating $6k/month despite having the lowest RPM I've seen so far (only making around $2 per 1000 visitors). Despite this the hosting cost was only $50/mo and I bet I could get that down to $15/month with even better performance.
Side note - you get paid commissions on everything people buy for a certain time after clicking your affiliate link. People buy tons of stuff on Amazon so you'll get lots of revenue for non-book things too.
If you want more info on this type of business model go look at these site (I am not affiliated with them at all):
https://thewebsiteflip.com/
https://fatstacksblog.com/