Hey, although I haven't worked on a grow quite that big, I've been running a $15,000 3 room setup for about 18 months now. With 30k to spend, and 400 square feet, you can easily do 10 lbs per. Here are some key things to consider.
1) If you want big yields, you need co2. A co2 generator is a must.
2) Since you will be using co2, it is imperative that your HPS lamps have vented hoods. This way you can still keep your room pretty cool, while making sure it is airtight for the co2.
3) although with such a large budget, it might be tempting to do hydro, i recommend soil for something this size. I'd recommend setting up soil pots, and then using a drip irrigation system. If you don't do this, watering your plants will become a NIGHTMARE. Also, soil doesn't really overheat like a water system does; again this makes it easier to use co2 and increase yields.
4) whatever it is you decide to do, budget 1.5 times what you think it will cost. Even the most experienced growers will make the occasional mistake...each set up is unique, and there will always be a bit of trial and error to get things working properly.
5) If you haven't already, find an electrician and someone that has a working knowledge of carpentry. You will definitely need to do some rewiring, and it will take someone who is handy with saws and drills to create the substructure you will need to support vents, lamps, ballasts, etc.
If you have some more specific questions, just msg. me! Here are some pics of my flower room to reference!