Next time you decide to attempt Arch, you could try the included install script.

But for now I would also suggest starting out with something more simple, such as Linux Mint or Ubuntu LTS.

That's what I thought as well.

If you just clone the repo there will not be any sources from the AGPL:ed source within the project, only a text mentioning the name.

However if you build it locally, it will pull in the third party libraries. So as long as they aren't distributing any built packages without a AGPL-compatible license, I don't think they are doing anything wrong.

(IANAL)

dark theme could be darker

Try the "Amoled" theme in the settings (remember to click save at the bottom of the page, I initially missed that). It's a much darker theme on my phone.