I'd go with a 6 bulb fixture if you are going with t5's. Keep in mind that bulbs are going to run about $120 a year pulse the initial cost of the fixture. Power consumption when all on on 8-10hrs is 324watts. Say you went with a reef breeders photon (programable & dimable) your initial investment about $450 total power consumed 97watts full power which you would most likely not ever have them set to full power. With the savings on power and bulb replacement every year and energy savings a led fixture would pay for it self in 2-3yrs.
Then I had my 75 gal tank it wasn't drilled and that was the biggest mistake I made with that thank and the main reason I upgraded to a larger tank. On my 75 I decided I wanted a sump and did a hang on back overflow box. I was on vacation and it had lost its siphon and the main tank overflowed. Thank god I had a Apex controller and knew something wan not right and was able to shut down the return pump and have some go to the house and check it out. My new tank has dual overflows with emergency overflow pipes too. Nothing like pice of mind.
I was looking through some of your other threads your tank looks pretty darn good.