grow space question?

yea i plan on using a 400w hps, but my grow space is already pretty small 4x2x6'' and i'm wondering if i should even use a box since it will probably only make more heat, or should i just grow on the floor? if i grow on the floor i was planning on getting some mylar for the walls, but i was wondering should i also put it on the floor beneath the plants, or will this make more heat go to the bulb? also i was wondering if i'm wanting to sex my plants earlier than waiting for the preflowers, how high do they have to be before u can do this? and do i just take a microscope and look at the internode growth? male=clusters, female=hairs? also i posted earlier about some digital ballast's and i'm not sure what kind of sockets they need or what kind of reflectors that they are compatible with, one of them already has a socket but i'm not sure what kind of reflector it will work with? here they are again http://cgi.ebay.com/400w-HPS-Digita...9444572QQihZ014QQcategoryZ42225QQcmdZViewItem
http://cgi.ebay.com/New-400-watt-Hp...hZ010QQcategoryZ42225QQtcZphotoQQcmdZViewItem
http://cgi.ebay.com/400-watt-DIGITA...ryZ42225QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
if anyone could just tell me what kind of sockets and ballast's that are compatible for these ballast's i would appreciate it, and if anyone knows where i can get any of these compatible components as well...thanks for any help...