50 gal led questions

posted this in the diy section but guess this would be the better place for my questions.

hi everyone, i have an aquaone 980t which i have been slowly modifying from the useless spec of the standard tank. currently i have a 24" wavepoint 4xt5 fixture and co2/ferts but i have always wanted to try LED's the tank is 40"wx20"Dx28"H near as damn it. i have worked out i would need around 40 led's and will be buying the cree xt-e cool/neutral whites and then xp-e reds and blues.

i was wondering what width/length heatsink i would need and how would i space the leds to distribute the colour etc? would two or three rows of each colour work?
what would be best?

lots of questions i do apologise
thanks