Fenders+1
The "extra" posts keep the pannier from going into the spokes and possibly add support and strength to the rack.
Bags or Baskets depends on what you want to do with them. Bags generally require packing, where baskets you just toss, whatever, in there. Bags offer some weather protection, baskets not so much. Baskets can lose smaller items, depending on the size of the mesh.
I have no knowledge of, or experience with bike computers.