Porting wordpress to html

I’ve got a website that I’ve got set up on wordpress currently for a customer, and I’m not really happy with the speed of the site.

I was able to get the wordpress site up, but my html skills are probably beginner to intermediate. I’m currently in a full stack html bootcamp, so that should help somewhat. As part of my learning, I figured I would try to recreate that website in HTML to see if it would be any faster. That’s created some general design questions, though:

1) WordPress has a whole admin page … is there something like that I should be creating in html5? Is there some premade admin modules that I can just add to the project?

2) What about security? In WordPress, I just add some security plugins and turn everything on, what’s the equivalent of that using html?

3) I’m having a hard time finding equivalents to a couple of major plugins the site uses. Galleries, and Event Calendar. The site uses extensive galleries, with 60+ images per gallery. So I don’t really want to have to write out the code to put each pic on the page (is that what devs do for large galleries?) Or is there a module I can install, and just point it to a directory, and it makes a gallery out of it?

3a) The Event calendar is also a big one. I’ve found some calendars I could install, but it’s unclear how they work. I don’t want end users adding things, I just want the admin to be able to, so I suppose I need an admin interface for adding events?