I agree with XSiVE about the optics. 40 is too tight. If you needed them at all, 60 would be as tight as I'd go. If you are doing a mixed tank, you could get away without using optics at all.

As for the number of LEDs you would need, at a minimum 36, in a 12x3 array. Meanwell ELN "D" drivers are about as easy as it gets with the least amount of parts. To get more of a Fiji Purple look, you would have to use warmer white LEDs. I advise against red LEDs as they can be extremely distracting.