I am planing on using a femtobuck with 4 or 5 of the 3W star LEDs in series. For all 5, according to the hookup guide, I would need 5 (leds) * 3.8 (foward voltage) + 2 (volts headroom) = 21.1V power supply. There are plenty of 24V power supplies available, but what amp rating do I need? Will a 24V 1A be enough or do I need a bigger one?
The Femtobuck will only draw 330mA (or 660 if you jumper it accordingly) for the whole series. As long as you have enough voltage to cover the Vf requirements you should be good.