^^^ sorry but i respectfully totally disagree. i personally like to buy what will be my final product the first time and not waste money on 600's to just upgrade later. if you do your homework and research and promptly post concerns here and figure out who to trust or at least wait for multiple responses so you can seen a general consensus in the correct answer to your question i think your good. your investment should match your ambition and RESEARCH. as long as those things align and you have some sense you'll be fine.
hellaWORD
the bigger you go the more potential issues but no one here knows what you're capable of but you man. that
sun system 2 is a 250w light right? it would help but to really get the most out of your 4 x 4 a 1k light would be ideal. you would have to air cool a 1k but as long as you do that the temps in the tent should stay within a acceptable range in a normal temperature home.
because your footprint is only 4 x 4 a single 1k would do more for you then multiple smaller lights. a 1k will adequately cover a 4 x 4 and the difference between that and your two lights is how deep into the plant a 1k light can penetrate and make good solid buds. you will get better bigger buds from the top of the plant to the bottom using that 1k then you would ever get with a 400 and a 250 or even 2 400's in that space because no matter how many 400's you have they just cant penetrate as far down the plant to make good buds as a 1k!
if i were you I'd start researching SCROG. i see lots of guys running a 400 for flower and using a screen and pulling good yields considering how big there light is. in growing there is no right or wrong way you pick methods you like and you dial that shit in to squeeze as much out of it as possible.
