I personally prefer software that I can understand more on my own without “help”, and that’s also simpler to configure. In PiVPN and most OpenVPN setups I’ve encountered these days it’s either several configuration steps, or a bunch of helper scripts. I feel that with WireGuard it’s fewer steps and all can be done manually. The configuration files are pretty bare bones and simple to understand. The fact that it uses a simple key exchange rather than having to setup certificates and certificate authorities also appeals to me. The ability for the iOS client to import QR codes is kinda handy too.
I’ll fully admit it doesn’t have 20 years of development, and may be lacking features, but for my simple home VPN setup I like it.
No, you’d only need to setup it up on the pi, and on the device that’s remote. Depending on the local device on your lan you might need to configure it to be accessible from the VPN. My printer for example isn’t remotely accessible, my cameras are. It just depends on the device on your lan.
I saw you mention this in a couple of other places in this thread. Keeping a spare SD card handy, with backups, and instructions for a restore is a good first step. Two pi’s is a better one. If you use pi zeros you can reduce your cost greatly.
Yes one NIC as well, in fact my setup is with one NIC on the VM. If you have a PC with two NICs then you can place the PC to act as your gateway. There a couple of ways to do this.