Lol absolutely everybody is advising you not to use 400's because it's so inefficient and lower yielding than even moving to 600s... I think you need to visit igrowpopcornexpensively.com
Love the way you're thinking. The only worry is nosy neighbours or buildings control popping round if things start looking a bit to construction-y. Maybe say you're building a swimming pool lol.
Air conditioning is what you want in that situation. A portable unit would probably be enough, but you will need to vent it outside somewhere or the heat just makes its way back in... Plus they're noisy and cost a fortune to run.
There's a helpline, the number is 911, just phone them, explain you're starting out growing and want your 'superior genetics' for free, they'll sort you out.