I've been using Manjaro, which almost boils down to using Arch. I can only provide a tentative answer to your question about keeping AUR up to date: I don't know all the ins and outs. I use an AUR Helper, if you will, called "Yay". It is fantastic! A command line tool the runs almost all pacman commands transparently, for the official distro and AUR packages. I only have learned a few options, the ones that I need to stay sane. AFAICR, it is possible to get a listing of packages installed from AUR. If not, Pamac-manager is, I think, installed with pamac, by default on Manjaro. The GUI enables me to enable various repositories, including AUR; and whether to check for AUR updates.
AFAICT, yay keeps AUR packages up to date. For almost all pacman commands/options, yay works as a transparent replacement for pacman. Unlike pacman (but similar to Yaourt, which it replaces) It does not require to use sudo to run, as a mere mortal, but does ask for a password later on.
I've had few problems, and cannot remember when I've needed to manually update a package from AUR. Maybe a few. No more PPDs for me. Damn! This distro works so well, I've gotten lazy.
Alan Davis