VPN - Subnet it connects you too?

So I have the wireguard VPN setup and it "seems" to be working.  IE it connects and does not show any errors.

What I am curious about is three things:

1. I have devices on my main LAN that I want access to.  Some of these devices use UDP others are TCP or both.   If my VPN is on a different subnet is it best to some how route those devices between the LAN and the VPN subnet?  I think this is the more secure way to go but I will be the only one using the VPN so wonder if it is really needed?
2. To save the complexity of the routing above is it possible to configure the VPN server to basically put my VPN connection on the same LAN subnet?   Doing this would make all of the devices directly available.  I am not sure how to make this work if it is possible.
3. Is it possible to use Tailscale client to talk to the wireguard server on the Firewalla?

So here is an example of what I want:

I have a digital loggers power switch which has a web interface.  Lets say this device is IP locked to 192.168.1.138 and I have it configured for HTTP access on port 8192.

When I connect to the VPN I want to be able to access this device.  Since the VPN seems to throw me on some other subnet, requests to that device at that 192.168 subnet don't work.

Either solution 1 or 2 above would solve the problem.  But honestly all of the devices I want access to have their own password protection so it seems like just getting the VPN on the LAN would make the simplest solution.

Any guidance would be much welcome!