I am about to install Devuan (Stable) with the KDE Desktop onto a desktop PC. I have a couple of questions, however.

(1) Is it OK if I use the Synaptic Package Manager (or Apper), whenever possible, to install software applications instead of FlatPak (or some other distribution system)?

Other distros, like Linux Mint, require that you use FlatPak. Using something else appears to cause problems. However, I don't like FlatPak, Snap, Discover, and other similar package managers. I would prefer to avoid them.

(2) Should I install ONLY ONE desktop environment? Or, can I install both KDE and GNOME?