Start a new game and at the world screen (where you pick your starting location) click the "Add X Colonists" button.
Tested with 200 pawns. Laggy but playable.
Tested with 500 pawns and the game's UI starts to disappear...
- automatically equip weapons: FindAGunDamnIt!
- set default outfits etc. for pawns: Better Pawn Control
- Growing Zone Priorities
- skip manually rescuing people: Rescuing Job (for 1.3 but still works)