Sounds like you might not have the right graphics drivers installed. For nvidia, you should be using the proprietary drivers. Iirc, mint has a nice GUI for changing graphics drivers, called driver manager or something like that.
I'm right behind you! The only people I haven't come out to yet are in the workplace and can't be ditched as easily if things go sour. I'm glad everything worked out well for you!
Yep, just pick the one closest to what you want, eg static site, reverse proxy, etc. Then remove the ssl stuff and get certbot to regenerate it with your new certificate. (Don't forgot ipv6 if you have it enabled on your system)
paccache can be configured to keep x amount of old packages and can be added as a pacman hook, so you never need to run that yourself!