The 1+ ton tank: 320 gallons

[akpoly]

Any and all help is appreciated!

So the boss found out I have some aquariums at home (a meager 17 gallon and 6 gallon) and he thought it would be fun for me to do a huge 320 gallon tank we have installed.

And I am asking for everyone's guidance on this since this is definitely not my home tanks.

Acrylic tank: 72" x 36" x 30" with built in overflow
Lighting: LED?
Filtration: Sump or Fluval FX5 or Eheim Pro 3?
Hardscape: ADA horn wood, rocks and gravel (unknown type)
Substrate: Decorative white sand
Flora: Unknown
Fuana: 7x Angelfish or Discus (center piece), 100x smaller schooling fish for background (2 or 3 different species)
Budget: $2,500 for everything (except the tank)

We will have walnut millwork around it to hide the edges. What the big guy looks like:




The area I have for equipment:




OVERFLOW!




Inside of the overflow...




So my first task is, how do I filter this thing?

This tank already has 2 holes drilled in the middle of the tank and 4 in the overflow. SUMP? I honestly do not know why there are 2 holes in the middle of the tank and 4 in the overflow. Can someone tell me what each of those holes were meant for? I can understand 2 holes in the tank, but not 6.

But if I went for a canister, I could just plumb the holes for the canister and plug the unused ones.