i am building a new growbox and need advice about the lighting

box size is 13,1*2,6

atm i have 2 growboxes with 400w hps

atm i am building a new box and i was wondering should i put 3*400 w hps or 2*600w?

height of the box will be 6,5 feet

so what kind of exhaust/intake should i have in a box size 2,6*13,1*6,5 ?

any1 ? plz help