homebox XL ventilation and ligthing questions(my plan is inside )help me

should i use screen over my girls ?
something that:



if i should,when should i put the screen over my girls after or before flowering? which week ?

not for your first grow mate. Just keep it simple and grow out a normal plant. the screen is used for different techniques where you manipulate the plants growth and poke bits through the screen to try and get several main tops (colas) to your plant.

peace,
ive been slowly setting up my 1st indoor grow, i have the home box xl 1.25x1.25x2m, 600watt hps reflectors and a digital lumatek ballast
so far ive got 1 spectrum axial 150mm fan, is this the correct size for the hometent exhaust slot? and should i be considering a fan for intake and should it be a different power than the exhaust, or visa versa, help would be appreciated
and im not running carbonfilters due to the strain being a low odour species