I would consider more light for 55 Sqft. Although I don't think you'll need 55 Sqft. for only 12 plants. For 12 I would consider a few lights instead of one.
To weedhound, I think steme has a point for the electrically inclined. I do great wiring but never schooled for it. If something were to break, even past your warrentee date, He could just replace say... a capacitor. Knowing how to test your individual pieces, and having built it yourself, You have the cheapest repair allowed.
From my exp. building computers, I can say that manufacturers often put a cheap component or two under there "schnazzy" design. So it stands to reason that picking all your own known components would be an advantage. It always has been with my PC.
On the otherhand, I buy complete setups. I don't want to deal with my own troubleshooting. I have way too many other things in my brain right now. But if I were to go large scale, I wouldn't waste money on some fancy sticker and a UL #.