Lighting:
LED's seem great, but I've always loved T5 and MH technologies.  This tank is now a mixed reef so I have to be kind to my LPS as well as giving light to the SPS that grew from the previous encrusted parts that stuck around.  Over my 75G tank I have 4x54W T5 HO bulbs.  I'm now using the Tek T5 retro with the reflectors, below is the par readings with a few light setups, check out the 4T5 one for the current state.  I'm running the lights 10 hours a day full power, with 2 hours of just one bank of two.

Filtration:
I use a 29G sump, but to keep things quiet I have a return of only 60GPH.  This will turn over the real water volume about once per hour.  I use a filter sock, I do this to try and raise NO3 which had always been 0, I also dose NO3 weekly to achieve a level above 0.  I find having NO3 has naturally suppressed P04 numbers.  The sump is basic, I use a Bubble Magnus Curve 5 running dry enough that it needs the cup emptied about once per week, and I have 1/4 cup Po4 remover in a mesh bag inside the sock which is replaced monthly.  I have an Ehiem pump for return and I monitor flow with the Apex.  This is great because I can kill things like the heater if flow drops below 5gph for some reason, that way I don't cook the sump because my return failed.

I like to target NO3 levels of 1, and PO4 below 0.1, I'm finding my PO4 value is usually 0.04 which is a touch low for this tank, but I enjoy only cleaning the glass every 4 days so I'm hesitant to change my methods.  

Now that some of my SPS are starting to come back, Kalk is simply not keeping up.  I just bought the DOS with the DDR from Neptune and I'm finding that I love it so far!  It's super easy to use, and way more accurate than dosing pumps of the past.  Plus I don't need to do math to figure out how many seconds equal 1 ML and all that.  I'm using Randy's Two-Part.  The formula that raises PH.

My sump used to have a Cheato fuge, now that has some anthelia in it that was getting too aggressive in the main tank.  I also plan to keep xenia down there and any other soft corals that come out of the main tank.  I have a small propellor pump down there for flow since the flow through the sump is so low.

Cooling:
Even with modest lighting, small pumps, and not many other things to add heat to the tank I need some cooling toward the end of the day.   Now that the tank is in my office the humidity with the doors closed and fans for cooling became a huge problem.  I share a wall with the garage, so I plumbed a 1/10 HP chiller through into there and it's doing a great job.  Plus with it being in the garage it keeps the heat and noise out of the house.