Grow Room Setup And Lighting

This is my first grow and have a few questions about lighting. I am currently using a space of 60" wide, 54" height, and 26" deep. I currently have a great flouro setup for my newly germinated plants. I plan on upgrading to an MH/HPS setup but I worried about which wattage to get. I am looking into a 400 watt but I have two questions: 1. Will there be too much heat to handle? (I plan on having proper ventilation with a portable AC, and ducts running into grow room from house AC) 2. Will the light spectrum of one 400 watt be large enough to cover feed three plants in 12" pots? If not, will buying two 175 watt systems or two 250 watt systems be more suitable for the width of my grow space? I have included a picture of my growroom with the flouro and my babies in their first pots after week one. I plan on transplanting into 12" pots.

400w would be more than enough for 3 plants. And if you have proper ventilation, heat shouldn't be a problem. Good luck with your babies.