Interface selection is not required. About the AP Channel, I did not change anything so just keep it default.
To check if the Wired Wireless Network is proper do the following:
Click on System --> Mesh --> Topology and you will see the Wired AP in Blue Colour on Top and Wireless AP in Orange Colour below and in the same line on the right hand side you will see an icon for Actions when you click on that you will see the Wired AP and if you want to Manually Select the Wired AP in case you have many then click on Disable Automatic Uplink and Manually select the Wired AP. But if you keep it Automatic it will select the nearest AP automatically and in case the nearest one is not working it will find the next one which is nearest and is working, that way your network will work even if one of the Wired AP is not functioning. If you select Manual and your Wired AP is not working it will not switch to the next one.
I am uploading the snapshot for your ready reference.
Let me know if it worked and if you have any further questions.