Thinking of buying the above for my Xbox with FS2020. Do I also need to have a mouse and keyboard, or the controller be sufficient? Thanks. (First time question! - please be gentle!)
You can get by with just the controller, but a mouse and keyboard certainly make things easier, especially the mouse.
Most people already have an old mouse and keyboard lying around. Why not try it and see? Any USB ones will work.
Welcome to the forums! 
Yes it will make quality of life that much better. I quickly found I needed a KB&M and was my first purchase after the yoke. You can get by without it, but it’s worth the $30-$40. Make sure you get a combo KB&M so that only one wireless dongle has to be used in one usb port/bus. I use a Logitech MK360. Go for the full size keyboard with numpad as well!
You’ll want to know about this issue as well when your mouse intermittently stops working. The fix is to open YouTube then go back to MSFS to reactive your mouse navigation. Apparently this bug is closed as Asobo couldn’t “replicate” so we are stuck with this. 
I’m a Turtle Beach V1 squirrel, check here
For XB it’s unique you can use the throttle along the flightstick too on XB. For stick with the V1 throttle quad(you just clamp the yoke off to the side). I’m on PC now but it’s extremely versatile on XB.
Any decent wireless (or wired) keyboard/mouse also works on XB. A typical Logitec keyboard/mouse combo only needs the one dongle.
You can keep adding onto it pedals/stick/etc and a couple quick release cheap brackets. Older pic of stick with the V1 throttle while still on XBSX…
In less than 2 minutes you can go from TP OV10 Bronco to Cessna 172 or back to a Cub or left stick SR22T, or fly from the ‘right seat’ should you choose. Like Lego controls.