i would go 12 leds and hang it roughly 10-12" from the water surface, you should be able to grow pretty much anything including sps in the tank with those over it. you can always have the light lower if you want more power. use 60 degree optics.
i have a 5.5g frag tank with 6 LEDs on it DIY retrofit and i can put anything in it.
you can get a heatsink with the size you need from heatsinkusa.com
Why do you have to hang it? I thought you only had do that with Metal Halides?
I read that LED's do not give off any heat.
you hang them to get better spread of the LED, no they will not add any heat to the tank. since LEDs are a beam light at say 60 degree (optic) you need to put it up high enough to have good overlap of the LEDs so your light coverage is increased. if you used no optics you could get away with a few inches above the tank, or if you wanted it right on the tank you would have to get more leds and spread them out to get better coverage. they are a beam light rather than an ambient light such as t5's. halides are also a beam light but with the large bulbs and reflectors it helps put them in between a beam and ambient light system.
Are there any fixtures that are already made and ready to go out of the box that you would recommend for a 10 Gallon?
they make them, but they will cost you a ton of money probably $300-$500, that is why DIY is so popular because you can build it for $150 or pay $400 for someone else to do it so why not save $250