The w tells pacman to download only and not install updates. Later in the console you can just run:
sudo pacman -Su
that install the already downloaded updates without synchronizing with the repositories
I’m also used to run:
sudo systemctl isolate multi-user
before updating to stop the graphic environment. It’s not necessary, but I feel that it’s safer for the desktop environment. Do it when you are in the console after logging out from the desktop environment
Yes, but probably not a good idea to have any core component built from the AUR. My AUR packages are just normal apps that I can update from the graphical pamac tool if I want (after I have updated the system from official repos)