Your approach won’t work if you’re behind carrier grade NAT or you can’t open ports. My landlord provides my internet so I use tailscale (with headscale on my long distance vps) to connect everything and it works great. It uses LAN when I’m home, and NAT punches when I’m elsewhere.

Entirely depends on who’s publishing the image. Many projects publish their own images, in which case you’re running their code regardless.

Yes but there are ways to protect against that. For instance you can configure Tailscale clients to only trust nodes that have been signed by trusted nodes, or something like that.