For the CPU: I have a AMD Ryzen 5 8600G in my TrueNAS Scale box, I use the integrated graphics for hardware transcoding in Jellyfin. If you don't need transcoding it's probably overkill.
For TrueNAS you'll also want a lot of RAM, as ZFS (the filesystem) gets faster with more ram by using it as a cache. My box has 32 GB, but 16 GB should also work, especially if you're going with SSD storage.
And don't go cheap on the power supply, get an efficient one from a good brand (I prefer BeQuiet).
You are roughly describing how Tailscale functions, give it a look