The 400 HPS/MH doesn't have the light penetration like a 1000 watt, so use that to your advantage.

Grow as many as you can in 6" square containers. Flip the light schedule to 12/12 when 6" tall. They will double almost triple in size during flowering. Some people will veg a rooted clone for 0-10 before flipping the lights to enduce flowering.

Good Luck.