I ran a group of five through a six-session campaign. My biggest issue was that conflicts got out of hand unless I scaled up the opposition accordingly (e.g. a group of crows are attacking a caravan; one group of mice fights off the crows while another group gets the survivors to safety). I really had to be on my game to keep everyone involved.
Your Players’ Turns will be interesting because on one hand the group will have half-a-dozen checks to go around at minimum, but only a couple players will have the chance to gain extra checks during the GM’s Turn unless they get into a conflict. That might leave some players wanting.
I’d say try dividing the group into teams of two to four and have them working at separate mission goals. Cut back and forth a lot so no one gets bored. Keep the characters geographically separated so they’re not stepping on each other during the Players’ Turn. Good luck, be sure to let us know how it goes.