Not a weird drilling at all. Do you know where your boss got the tank? My bet would be a salt water place. To get more flow, salties often have more holes drilled where the live rock piles will be so that they can hook up extra pumps to increase flow for the corals. One hole for intake and one hole for output with no filter just a pump.
Also regarding the four holes in the over flow, it's safer to have four small over flows than one large one in case an anemone moves into the overflow and blocks one of the pipes.
I'd go for the sump if the office can stand some noise (which can be minimized with a herbie standpipe.)
If the office is a real quiet place with people bothered by noise, I'd go with a large canister.
Cool, don't know much about salties but makes sense the way you described it. Knew they had to be a reason, no one builds a 320gal acrylic tank and drills it without knowing what they are doing. lol.