There's a fair amount of overlap between all of them, so if you want to Pareto minmax it, I would recommend starting with Refactoring UI, which should help provide practical solutions to many situations and get rid of the most egregious horrors you might commit.
Of course, UI design goes much deeper than anything those courses can teach, but they're a great start.
Only commenting about it as that site is a course about designing interfaces: to me the font on that site borderline is ridiculous, with the flat lines on the t/f/g, narrow L, an ampersand that looks like an 'e' with a long tail. Makes it hard to read
Legibility sometimes needs to be traded off for impact or other variable that matters more depending on the purpose.
He could have used Inter, like every other landing page on the internet these days, but then it wouldn't stand out.
These are the kinds of things that have more to do with graphic design and that incorporate other considerations than typical UI stuff.
There are big weird gaps everywhere, some of them have mouseovers which change my mouse cursor into something intended to be amusing but have no link.
The "This will/won't work if..." items seem to be links but clicking them just jumps me back to the top of the page.
The weird animation under "Pro", no idea what that's supposed to be telling me.
Company logos at the top. Used with permission, I wonder? They have mouseovers but don't seem to be links.
"5-star rating"? Really? Who from? I need more information for that to be remotely useful, should be a link. Let's say my HN post has a 5-star rating too * * * * *.
As a "beautiful and functional interface" I'm afraid the web page scores a 0/2, for me.