That should be it. Remember that if you use the HQI, you will need a glass UV shield. The mogul base bulbs, which I prefer has a shield built in to the bulb.
I don't think MH will ever go away entirely. With all of their drawbacks, they are very good for reef tank lighting.
I agree with this. The first aquarium I saw with MH was a 58 gallon Oceanic that was set up by Albert Thiel when he worked for Dupla. I watched him set it up. To me, there is just nothing like it. I actually have that old Sunpower Dupla fixture that Thiel installed on that tank. It needs to be reworked (ballasts are bad), but it was a cool fixture for the day.
Honestly, seeing that first tank as described above, the lighting is what impressed me the most.
20k is bluer.
Remember also that I am not using MH on my "new" build. LED & T5 this time around. Heat is the issue for me, but if I don't get the results I expect, it is back to MH & T5 for me.