hi ther and welcome to RIU
I think you mean a Scrog as a SoG means a sea of green, made out of many smaller plants, kind a hard with one plant
a scrog is a net/screen or similar you train your plant/s under/around to fill out the screen with Bud stands at a similar distance from the light (in a small place a Scrog works well)
35x35x80 is a bit on the small side, try 50x50x1m if possible
you won't need a intake ventilation, as you pull air out of the box it have to be replaced with some thing, after all we are still on Earth, simple physics, air going out will make a underpressure in the box and pull in air form every opening, so a passive intake will work just fine (only really hugh grow rooms use a intake to help replace air) instead use both 120mm fans to pull air out, HID lights do get hot, even small 70W
Ooh yea and here is a chart that give you a idea of the right distance from the bulbs even tho it don't have 70W on it
you do the math
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