400W will suffice for the plant count however I would not just brush off the heat issue with a couple of CPU fans. You will want to move a lot of air in order to keep smell down and that is gonna cost you dollars.

If you want to skimp on materials, your yield is gonna suffer.

I take it this is the first grow.
Hydro be tough for first time. Have you considered soil?
You are going to have about $800 in supplies to purchase. Ready for this?
8 plants will require 30 min of attention every two days. Who is gonna look after the ladies?

There is a closet growing section here, read it all...every post...

Carbon scrubber + CPU fans = now way
4-6" 275CFM axial fan + carbon scrubber + relatively air tight closet = less smell not no smell

Your third guy is gonna be pissed... Now he knows you are growing (he'll figure it out easy) and on top of that, now he is pissed, do you think he'll not tell anyone and everyone? Do NOT be stupid about this.

Parents will not support this. Don't kid me or yourself.

Remember the shit is illegal.

Enough for now.
Read, read, read......and then plant a seed.