gannmann9876 - There are a few things to look at when buying parts. I've tried to quickly skim the thread and would like to throw in my 2 cents, if it helps.
Buying a kit is fine, however, like suggested, sometimes it might be better to buy the parts individually. I've bought from RapidLED and ETG Tech. ETG Tech may ultimately end up being the best price as they are one of the major suppliers of the LEDs to most of the online diy stores. There might be a minimum order though. It's been a while since I ordered from them, so you may want to check.
In addition, the kit is supplying only CW and RB LEDs. What people have been discovering is that there is a loss in coral coloration when only using those two dies. So people are now experimenting a mixture of CW, RB, neutral whites, warm whites, and regular blues to increase the spectrum and bring out the color. I haven't gotten the chance to run those colors yet but I am running a red LED. Brandon knows more about this and can probably give better advice.
I've currently been running a 1:1 CW:RB set up. I would say it's about 10-14k, depending on which MH bulb you're comparing
I like the look of the color personally as it's pretty crisp. A 60/40 mixture is will probably look nice as well.
On the question of whether or not 72 LEDs is enough. LEDs aren't about watts per gallon IMO. The thing with LEDs is that you need a sufficient number to maximize the spread. It works differently than MHs in which are an intense point source. Various factors come into play like the optics you are using and how high the fixture will be off the top of your tank. For instance, if you are using 40 optics, then you will need to space the LED's closer together. In that case, you will need more LEDs to cover the spread.
In addition, optics are what drives the intensity of the LEDs. The more narrow the optics, the more intense they will be. For comparison, a 250w MH will be similar to LEDs with 40-60 degree optics. 150w MH will be around 60-80ish. You will need more narrow optics the deeper down you go. So if you have a tall tank, then you may want at least 60-80 degree optics. But then again, this will also depend on the type of corals that you were wanting to keep. Good thing about optics is that they are easily replaceable and relatively cheap to switch out.
About the heat sink, look at HeatsinkUSA and compare prices. That's where most of the online stores are getting their heat sinks and they carry a 10" wide one.
