The only figure I am missing is the Walmart Exclusive Will in his variant Upside Down mode.
First up - Series 3 which includes Mike and Will from Season 1 and Eleven from Season 2.
Second - actually backtracking to Series 2 from Season 1 - Lucas and Dustin.
Here is the unpackaged Ghostbuster four pack. Awesome!
And now for the gang from Season 1.