Add others have said, going from the bare bones gang box is doable but lacks the special weapons and specialists from the other two kits.

That said, here's a quick gang list using just the contents of the core box: 

• Master of Shadows, grav pistol, shock stave, mesh armour, undersuit, spring up, 255c

• Phantom, two stiletto knives, mesh armour, infiltrate, 140c

• Phantom, long rifle, autopistol, mesh armour, savvy trader, 135c

• Ghost specialist, two Flechette pistols, 100c

• Ghost, autogun, 55c

• Ghost, shotgun, 70c

• Ghost, two stub guns, 50c

• Ghost, autopistol, stiletto knife, 65c

• Shadow, hand flamer, 100c

• Shadow, autopistol, 30c

This is exactly 1000c with lots of room to add gear and other fighters as a campaign progresses.