Stupid space...

I have box widh 60cm depth 40cm and height 70 cm,so is 400w too much for that space or not I have cool tube? And how much (autoflower) plants can I put in that box?

If it was taller, you could get away with it, but being so short, I think a 400w is way overkill, that's like 100watts for every 25 cm2, where optimal is usually averages about 50watts.

Heat is just going to cook you out even with the cooltube. A 250w or 150w would be stellar

Agree ! ^^^