I think a Company will wind up being the right size. We'll need support for the vehicles and gear, and if we're going to run electronics then tech and support for that. Some of the teams may be NPC driven, perhaps each PC has an "action" team and also a "support" team to manage so Frank/shaidar doesn't have to do it all.
Addendum Using the
German Boxer as a design prototype, crew of three plus up to eight troops. So, one combat squad carried and one fire-team with the vehicle. Two vehicles carries a platoon, and we need one vehicle for mobile command post (MCP). Adding platoons of two vehicles doesn't require another MCP, but a far vehicle (ship, ship's boat) with data analysts and medical facilities is required. All of those vehicles need support crews and machinery to support. Perhaps depot level maintenance back at Collace, but that's still staff in the unit.
An alternative would be more training and diverse skills, so that vehicles could be gotten "on site" and maintenance not be an issue. That would allow for a smaller head count unit and lean towards a more elite unit.
As an aside, having a "back area" where invalidated out staff can go is a plus. If SEMC is running a training section then that means a trooper who loses an arm or a leg isn't tossed aside.