Something like a FT240-43 toroid should work for 80m to 10m.

That is to make a common-mode choke on your feedline. You can always try to improve the RFI emissions from devices in your house by snapping on some ferrite on wall warts etc.

The main job of the unun is to match the impedance of the wire to the 50ohm feedline. You may or may not need a common mode choke to prevent RFI, but I had a lot of RF problems with my 40-10 EFHW. My radio was fine but my computer started to glitch out when was transmitting. That all disappeared once I looped my feedline through some ferrite.

Awesome! If you do plan on transmitting (on 10m), I recommend a common-mode choke on the feedline between your radio and the EFHW. All you need is a ferrite toroid and loop the feedline a few times through it. This can prevent RF going into your shack, which is kind of a thing with EFHW antennas. Otherwise EFHWs can work very well. Have fun and enjoy your new radio.