They'll have been working on Firewall since prior to this adventure - for this group, if we only get 4, I'm applying to character creation a set of rules I call 'Experienced Sentinel' creation. If we get 5, we'll have the usual. If it's just the 4 of you, you've done 2d5 missions for Firewall, if 5, then only 1d5. Also, you will have other Firewall Sentinels in the group at certain points if you lack a certain attribute, background, or so on.
And before you go asking, this campaign will span pretty much the entire range of planets - Sunward, the Main Belt, Rimward, probably even a couple of exoplanets.