On my BC14 I did 16 - 3W LEDs.
8 RB
4 CW
4 TV
2 RGB chips
All LEDs were on 3-up stars, except for the true violets, so as to minimize the disco effect. For you I'd atleast double the number I used (depending what you want to grow - I grow SPS). The RGB make a HUGE difference in rounding out the colour. With the RGB I can get the colour temperature very close to my 250W 14,000k Pheonix bulb. Without the RGB it find it looks washed out and lacks the vibrancy that metal halides have.
For numbers of LEDS and layouts, check here:
http://www.nano-reef.com/topic/31199...m-led-layouts/