Using ethernet for iMac and Wi-Fi for other devices I now use Wi-Fi for my iMac and for various other devices. Can I set up the iMac to use ethernet directly w/o Wi-Fi involvement and have the Wi-Fi continue to connect for iPads, TV and smart phones? Concerned about security as I do banking and other financial stuff only on the iMac.
Usually it's no problem to use the ethernet interface instead of the Wi-Fi interface, if the router/access point contains one or several ethernet connectors:


Install an ethernet cable between your iMac and the router. Depending on your router you might have to enable/configure its ethernet interfaces.
Open System Preferences -> Network.
Configure IPv4 of the ethernet interface by choosing DHCP or Manually. If you've chosen "Manually" enter an appropriate IPv4 address, netmask, gateway and DNS-server
Click on the gear in the lower left corner -> Set Service Order..., drag the ethernet interface to the top of the list and click OK.
Optionally you may deactivate Wi-Fi by highlighting it in the left pane and then "Turn Wi-Fi off"
Then hit Apply