I like 600s (just a shame I haven't anywhere to run mine at the moment
).
The reason I mentioned 4x600 was even light-coverage. I can't see how you would achieve an even footprint with 3 lights in a square tent.
Personally, I would be thinking of a 1x1 tent with a 250MH for veg and a 2x1 tent with 2 600HPS for flower. Do a scrog and use hydro.
It sounds like you have a decent amount of cash to start. It's a good thing. In this, more than probably any other hobby, buy wisely, buy quality, buy once.
Especially with ventilation.
If it were me, I would buy a 1x1 now with a 250MH, 6"RVK fan, hydro kit and start vegging 4 fem seeds.
If all goes well, buy a 600hps and put that in there.
If all goes very well and you decide to do this on the larger scale, buy 2 600hps, an extra hydro table and the 1x2 tent and a 6" or 8" fan (you can now swap out the 6" you bought earlier as needed). Learn to clone.
If all goes crap, and you decide it's not the hobby for you, at least you haven't wasted too much money.