Added note… Ray did suggest you used the TL-Link as a access point but I missed that comment… as you seem to be moving towards using Ethernet.
Just to add some more detail about Access Points and there ability to act as an extension to or even exstend the range of your home internet router.
Once you have this new network setup and you have made changes to your raspberry pi(s) with their new IP address. You can then forget about them being on a different network, as with the WAN connection between the AP adapter and your home internet router… any IP address on this new network can be seen from your home router network even with them being with different network addresses. Therefore, this means your new home owner doesn’t need to know anything about setting IP address or changing WiFi setting. He just needs to know how use the OpenSpinkler APP…(give him the user name a password for the wifi AP adapter just in case he needs to change anything)
Example my main controller was on 192.168.1.21 and my slave was put onto 192.168.10.122 I could access and control both of them on my OpenSprinkler App on my iPad
One thing I haven’t yet solved is how to get port forwarding to work from this new network.