> Do you mean if I add a hashtag to a post, then, on the site I can enable or disable certain hashtags?

Yes you can choose certain hashtags that should show up on the site, and then if you include a corresponding hashtag in your post it will appear on the site.

> What happens if I don’t add a hashtag to a post, is there a way to prevent it from showing on the site? 

If you choose specific hashtags to show on the site then posts without those hashtags won't show up. You can omit hashtags in site settings and then everything will show up.

> When I mean a regular website, I mean something like I currently have, where I can design my own pages

Npub.pro sites use Ghost themes, which means you can take existing Ghost theme or create a new one with custom design, publish it and use it. We don't have good tools/UI for that yet, but if you need it soon we will push it.  

> add educational materials (like PDF slide decks that I have created), 

You just upload those PDFs to some media server (nostr.build?) and then include a link to PDF in your post.

> add buttons that open pages or content, 

You can customize navigation menus and add links to any page or content in site settings, you can also use code injections to add anything imaginable to header/footer (and potentially any other place with a bit of code).

> change the background color, and other things like that.

Code injections can be used for that. There's no UI for it, you'd have to code it. But then you could just post your needs on nostr and somebody (me for now) can help. There are lots of bored devs out there :) 

Hope you give us a chance and we'll try to improve things for you!