you can use different aluminum fixtures to spread your LED's no real need for heatsinks and fans. unless they are highly concentrated on one heatsink.
Heatsinks will make your LEDs last longer and use less electricity per lumen. So I would recommend them.
I have read on some reef forums that one reason LED fixtures are already not commercially available in the US, is that a certain company holds the patent for LEDs used for aquatic growth (or some such nonsense) and they have been very active suing smaller companies that try to sell them. Thats why there are lots of sites (like rapidleds.com) that sell kits but don't sell fixtures.