So, the big thing with instability is that with Linux “Unstable” refers to “Constantly receiving updates” rather than “Breaks all the time”
In my experience, if arch breaks, 99% of the time YOU the user did it.
If you want a kinkless experience with it, keep it simple.
Arch ships with systemd, as such, it also ships with systemd-boot. Use what’s built, don’t add additional bootloaders unless you need the functionality they offer.
Gnome, Matlab, and VScode have wiki pages for installation and configuration, and Firefox is in the repos and is one line in the terminal to install (#pacman -S firefox)
For a first install, I’d recommend following the wiki to install instead of using archinstall to familiarize yourself with how to use and read the wiki.