Arch Wiki is your friend and a fantastic resource.
Learn pacman inside out, best package manager in penguin land.
https://wiki.archlinux.org/title/Pacman
Understanding how to define (PKGBUILD) and build (makgepkg) packages definitely helps.
https://wiki.archlinux.org/title/PKGBUILD
https://wiki.archlinux.org/title/Makepkg
Arch User Repository.
https://wiki.archlinux.org/title/Arch_User_Repository
Fantastic tool, so many packages in one location, easy to use.
Just be careful though as all these packages are user maintained. Each AUR package has its own web page. Read it first. AUR package comments, PKGBUILDs and source help determine a level of trust in an AUR package.
As Arch is a rolling system you’ll need to maintain it to keep it healthy in the long term. Install once, maintain indefinitely.
https://wiki.archlinux.org/title/System_maintenance
If you are looking for apps to do certain tasks, this may help.
https://wiki.archlinux.org/title/List_of_Applications
If you need / want access to older lts kernels and lts nvidia drivers use this.
Unofficial repo for older LTS kernels
And finally you’ll need a tested backup / restore process; and be familiar with chrooting into a system through a live environment to fix issues that require it.
You won’t need these often, but Arch is bleeding edge so you’ll probably need them eventually.
Have fun!