I would go with EITHER the T5s for vegging OR the dual ballast--you do not need both. In a space that size, I do not believe that I would put T5s on the walls. You would be far better off with a 600W and forgetting the vertical lighting. It is not a new or novel idea and in some instances may be a good idea (my own opinion is that vertical lighting has very little benefit). However with your 3 x 3 x 6' space I believe that it would actually be detrimental--you will lose much needed growing space--probably a third of your growing space. In addition an investment of 4 4' 4 tube T5s would be around $600. While it may look "boss", you really would be giving up far more than you would be gaining. Start with the basics--3000 lumens/sq ft of blue light for vegging, 5000 lumens/sq ft or red light for flowering, adequate ventilation, good soil mixture, nutes formulated for mj, etc, etc. and get a few grows under your belt.
I personally own a couple of MH lights that I do not use at all anymore, preferring the T5s for vegging. However if you purchase a dual or digital ballast, you will only need the one fixture and 2 bulbs. The T5 is an entirely different setup. Also, not all T5s are the same. Look for the HO fixture and tubes--4' 54W 5000 lumens per tube.
While a 400W will do a 3 x 3 space, I would go with a 600W in an air cooled hood or cool tube. You can get digital ballasts that are adjustable. I have a 600W that I can run at 360W, 400W, 600W or super lumens (whatever that is). Right now I am running the 600W in a smaller space (about 2 x 3) and running it 24/7 at 400W. When I go to flowering, I will turn it up to 600W. Do your homework and buy smart. Most of us that have been growing any amount of years have a "storeroom" of unused equipment, some of it simply not well thought out.
You are also going to need ventilation--a good quality centrifuge type fan to exchange air and keep your space cool. You may also need a carbon filter for odor control.
Unless you plant is sexed, I would highly recommend sprouting several more seeds--at least 4 more. You are going to hate it if you baby this plant for 6-8 weeks only to find out it is male. In addition, if these are bagseed, keep a sharp eye out for hermies when you get into flowering.