How much cfms? which light? and good tent or not?

Ok so my first harvest is just around the corner and its going to get me some more funds to expand my grow. I have a 250 watt digital HPS with MH conversion. I want to have around 600 watts though, one question is

Should i buy a 400 watt lumatek and use it with the 250 watt i have now or just buy a 600 watt lumatek and put the 250 in storage? I dont wanna go above 650 watts power usage.


Now second i was wondering if this is a good tent? It is off ebay for 90 bucks! and is the perfect size for me. I didnt wanna post the link cause i dont think im supposed to.




4x4x6.5 FT HYDROPONICS GROW TENT HYDRO BOX HUT CABINET



Next i would like to talk air flow, how much cfms of exhaust and intake would i need for the above tent and 600-650 watts of HPS?

Last question:
What is the best type of reflector for easy cooling?


Im using ebay for the tent, and cheaphydropnics.com for the light, and im not sure about the fans yet but maybe HTGsupply.com.

thanks in advance if you help me

I would go with the 600, for a two reasons...

1- heat from one lamp is going to be less than two( 2 bulbs= more surface area and in turn more heat)

2- The 600 offers you better light. (same concept as the heat.. the 600 will offer you a more intense light evenly throughout your space, using a 250 and a 400 not only creates uneven light within your space and the light intensity is a fraction of the lumens offered by the 600.

so im pretty stoned.. not sure if that all made sense, let me know if you need anything else