Ports below 1000 or something are reserved for root by default.
Take a look at K3S if you plan to use kubernetes on a single node.
a small PC with kodi can do this. It can do much more as well.
it depends which device you get. Some routers are much better then others at routing. i think you want to look at the CCR series.
For automated backups defiantly. For a one time use I often use just rsync. It is the simplest to quickly use.