I'd really like to try to plug a different device into the barn side.  Anything that has an ethernet port that needs to connect to the internet and/or can be accessed via IP address.

I don't have any devices on the software version you are running.  On your Barn device under the advanced settings there is a setting for Bridge.  If you click on the edit button for that do you have any options?  Are both the WLAN and LAN part of the Bridge?  I'm grasping at straws right now.