Seems like a nice bike to roll. — I like your panniers :-)
Usually I go with one pannier. But this year, I might choose to add the other one, to have an extra lightweight insulated jacket for emergencies on the road (or at my work space).
In the early years I commuted with a backpack. But from the moment I had to cycle a longer distance, I preferred to have my back free.
I do carry a very small backpack in my pannier though. Contains my lunch and some small things.