It should be the same setup regardless if you're using a VPN or not.

Having used both I generally prefer traefik.

You're gonna need to provide more detail on what you're trying to do

You can restrict Caddy access to use your tailscale. For instance in your Caddyfile:

For tailscale ip range:

myverycoolserver.duckdns.org {
    @allowed {
        remote_ip 100.64.0.0/10  # Allow Tailscale IP range
    }
    respond @allowed 200  # Allow access
    respond 403  # Deny access for others
    reverse_proxy localhost:YOUR_SERVICE_PORT  # Your service configuration
}

For specific tailscale IP:

myverycoolserver.duckdns.org {
    @allowed {
        remote_ip YOUR_TAILSCALE_IP  # Replace with the specific Tailscale IP
    }
    respond @allowed 200  # Allow access
    respond 403  # Deny access for others
    reverse_proxy localhost:YOUR_SERVICE_PORT  # Your service configuration
}

Might look into the pangolin project if what you're trying to do is expose services from your home network over wireguard to a reverse proxy on a vps.
The software suite is basically wireguard, traefik, and auth middleware wrapped in a trenchcoat. Much simpler than rolling your own implementation, but there has been recent controversy with the project over locking "basic" existing features behind a paywall after the project got popular, though after public backlash they've backpedaled on that iirc.

Edit: Just realized you said tailscale. Above recommendation might be a deal breaker depending on your reason for wanting tailscale specifically

I have caddy on a vps that serves as a tailscale exit node and also reverse proxies over the tailnet. My pfsense router is also in the tailnet and exposes some subnet ip addresses to the tailnet. So for example I have public domain watch.example.com hits my caddy and gets proxied to internal IP 192.168.31.48 which is my jellyfin docker.