I'm not quite sure about if your still planing to do only half but if you are, and this were my space, I would probably go with the following:
600 watt light with a larger air cooled hood. DO YOUR RESEARCH ON HOODS!! there are huge differences. Becuase your so narrow, You may want to get a long Jumbo hood (like the magnum XXXL). A traditional sized hood would be put in perpendicular to the long edge of the garden, you might have problems running the air cooling ducts to it. hence my suggestion for the bigger hood.
The 600 is going to give you much more light to work with which means larger, tighter, and frostier buds. The 600 watt is also THE most efficient bulb in terms of lumens/watt.
You will have an inline fan that pulls air from the adjacent room , runs through the hood, and exits outside the room.
If this is your first time hydro I would really steer you away from DWC. I know it seems cool and all but it isn't the easiest hydro format to work with and this being your first time, you may just fuck things up. I would suggest a ebb/flow system. I really like the bucket based system but you probably don't have the cash for that. You can build a simple flood table for about $50 in parts. Much easier to deal with than DWC, specially in a narrow space like yours.
Cover all the walls in mylar as it will really boost the amount of light your plants are using in that narrow space.
6 plants is probably going to max you out in terms of space. top the plants once (fimming would be better if you can do it correctly) and flip them to flower when they are about 18" tall.
Depending on the plant you'll get about 10 pounds from that set up. LOL Seriously though, if you train the plants and don't screw anything up you should easily get 3 oz per plant.
Cheers
LF