Welcome - beware of the dragons - former Ubuntu users usually takes time when introduced to pacman, AUR, makepkg and Manjaro’s inhouse package manager Pamac.
Arch based distributions don’t have PPAs but AUR - take your time to get aquainted with Manjaro and the maintenance of Manjaro before you dive into building packages from AUR.
KDE and Gnome is known to introduce hard to solve issues for newcomers to Arch based distributions.
Xfce is recommended to get your feet wet.
Recommended reading