[zombietots]

I would like to find the recommended order for the Missions (Season 4), Artifacts, Horizon, and Boardroom backstab, plus the campaigns. What is the timeline on these products, where should I start?

[Mantis]

Artifacts first, then you can mix in Missions, Horizon and Boardroom as far as being published first and the stuff in Artifacts is supposed to happen before the others time-line wise. However, tossing a bunch of brand new characters into Artifacts can easily lead to a bunch of dead brand new characters. I'd advise you run maybe half of the Season 4 missions first, or all of Season 3 to get them experience before diving into Artifacts.

[raggedhalo]

The four Dawn of the Artifacts missions are set in early 2072 (but are rock solid!).  Bull's said elsewhere that Missions Season 4 adventures are intended to take place one a month, from January to December of 2073 inclusive.  Then it's basically order of publication for Twilight Horizon and the Boardroom Backstabs missions, but you might want to switch up the order you run the TH adventures to suit your group.