Verified answer

How many Operators can you have in Zero Company?

Officially documented mechanics, with version and uncertainty kept visible.

Keep the four roster rules separate

HQ capacity
Up to 20 Operators
Starting roster
A maximum of seven Operators
Standard squad
Up to four Operators
Hawks deployment
Required for story missions; skirmish missions allow any combination of Operators.

Mission exception

Certain missions can add controllable characters beyond the standard deployed squad limit. The Q&A also says Hawks is required for story missions, while skirmish missions permit any combination of Operators.

Sources and evidence