Michael Lucas released a stellar book on the subject not long ago (https://www.tiltedwindmillpress.com/product/ryoms/). It’s pretty thorough, relatively up-to-date, and (like all his stuff) a fun read. It does a great job of demystifying the mechanics. As far as the implementation goes, I’ll put in another vote for Mailcow, which combines all of the components into a very usable docker stack.
Yeah, I sort of figured it’d be too much. It looks like there are a bunch of booking plugins for Wordpress. That’s definitely where I’d start my search in your shoes.
I’ve been using Odoo CE for some projects and I know that it has apps for scheduling and booking, but if you want to add this to an existing website, that may be overkill.
What platform does your site use? That may help target some suitable options.
Also, check out this list and you may get some ideas: https://github.com/awesome-selfhosted/awesome-selfhosted?tab=readme-ov-file#booking-and-scheduling
Not sure about a PDF, but he sells an epub that’s $15 US.