First time grow tent-Need advice

I was thinking of buying a grow tent but i am completly new to this kind of equipment
I was thinking of a 6*2,5*2,5 (feet) grow tent (its the maximum space i can use)
400W Philips son t agro dual spectrum+reflector,ballast etc
2fans inside the tent for cooling
1intake fan-1 outake fan

What else do i need?
How many plants can i stick in there?
I saw in many grows, a tube attached to the hps system, is this necessary?

2 plants are enough for me, i dont want an expert setup so please suggest the absolutely necessary equipment
I already have ph meter,timer

The "tube" is a ventilation system. It sucks out the hot air directly from the light bulb and out of the tent. Often the air goes through a carbon filter which will clean the air so it doesn't smell like MJ. IDK if you need a system like this, but it is better to have than not. The main concern you will have will probably be heat, the fans inside the tent only move the air around inside. If the air is too hot it won't do much good.

If the temperature is about 65F outside the tent, could i manage to keep it around 78-80F (with 2 outtake fans) inside the tent?

ummm im a lil confused at how big ur tent is is it 6x5x5? if its that big u wouldn't need the whole set up for the light to keep it cool, as long as u have the fans inside the tent, r u planning hydro or soil, do u know what u'll need for soil mix, and ferts if u wanna use any?Also if by any chance Im just stoned and cannot read and ur grow room is smaller and ur worried about heat u could also look into LED lights(expensive) they r supposed to be quiet good and put off very little heat or T5(cheaper) and then cfls(cheapest).

My space is 1,8Meters high (5.91 feet) 0,78 meters wide and deep (2.56 feet)
I plan to grow in soil. I have biobizz all mix with all of their ferts. I am using cfl's at the moment but i am not satisfied with the yields,so i may choose hps.
the main issue is if i am going to make it with this setup.I mean what temperatures i should expect?! will it be enough for 4 plants in 7,4L(2gallon)pots? If i pull out an oz of each plant i will be satisfied

Im not really sure how hot using a HID light would make it in a tent that size but with the intake and outtake fans and ur tent seems tall enough that the light wont be right on top of the plants. And usually u don't want temps to go over 85 degrees.