Your Help? Possible Grow Room set up

Hello havent posted here in a while. I need your help and opinions (even if they are negative ones)

I just got my card and here in northern cali i can grow up to 6 mature plants.

heres what i want to do.

i have a mother-in-law cottage in my back yard that has about a 4.5ft x 3ft x 8fthigh space i want to grow 6 plants(3x2).

I would like to use a 400w hps.

for ventelation and cooling i was going to cut a hole in the wall for a wall AC that can cool a room in secs.

now a couple questions u could answer.

-i live in northern cali, where temps in the winter are as low as 30f and as high as 100f in the summer. In the winter would i need a small heater at night? In the summer would the wall AC be suffciant for cooling(there is currently now AC in the cottage)? your suggestions.

-your recomendation on lighting? 400w hps or 600w, etc? cfls for sprouting?

-what could i expect for a yield? 6 plants under an hps. is 1.5 oz per plant realistic?

thanks in advance.

-ty

get a 1000 watt and good exhaust.