Anything I should do after my first Linux install?

I’d keep the first round boring: install updates through the system’s normal updater, check that Wi-Fi, sound, sleep, and any other hardware you rely on work, then set up a backup for your files. That gives you a solid baseline before you start changing things.

For software, stick to the distribution’s usual sources unless you have a specific reason to add another one. You can always customize more later, and it’s easier to figure out what caused a problem when you haven’t changed ten things at once.

If KDE feels good, keep it. Eight gigabytes by itself doesn’t mean you need to switch desktops. If things feel sluggish, check what’s using memory while you have your usual apps open. A lighter desktop is an option to try, not a requirement.

And I wouldn’t assume a slow-feeling LXQt session was necessarily caused by X11. Session settings, graphics support, and what was running could all affect how it felt.

For programming, install only the tools your current projects call for. A version control tool, your editor, and the relevant language tools are a reasonable start. Follow the documentation for the project or language you’re using rather than collecting a pile of packages from unrelated setup guides.

The visual tweaks are fine too, but I’d save a note of what you changed. If something gets odd later, you’ll have a short list to check instead of having to remember every setting.