Mach - are you in the states? If so - i would NOT cross the 99 plant limit... be careful - you're steppin' on the feds toes there...
I try to keep my numbers low... i only have 4 plants right now - i'm expecting over 1lb with a 1k light.
i set up my own system... DWC, with 5 gal buckets - i did it on the cheap, it was not over $700 i know.. maybe like $150ish for 4 buckets. (air pumps, airline, water pumps, vinyl tubing, connectors, res, float switches)
if you are going to go with a pre-built system... i have a friend who swears by this
http://www.discounthydro.com/systems.asp#EG12 ebb& grow system...
the key to the weight you are looking for is definately light. I would count on 1 lb from every 1k - and if you get more than that - you should feel lucky. you can get to 2 lbs per 1k - but thats hitting the 1 gram per watt efficiency, which most people cant do - and you'd be hard pressed to do that on your first run... so if you want 4 lbs every month, you'd want 8K in flower and you'd need a cabinet for some clones, you can just fill 1/2 the system 1 month, then the other half in another month... and you're set.
although 8K is a rediculous amount for a 1 bedroom apt, and you'd eventually be able to get more than 4 lbs per month... thats just a lot of herb. :D
peace