My main battery will be a 4 Sell lipo, so battery voltage will be between 14.8 to 16.8 (as the battery drains), though I am open to putting in a separate 3 sell (11.1 to 12.6v).
The layout I am planning is 3 of the 3w's upfront to be a headlight, so they can be pwm'd as a group and would be ideal for a series, 2 of them will be mounted on either side of the fuse to light up the wings as well as provide flood and landing light, they could be series too, then there will be 1 1w on each wing tip (red/green).
I have been thinking about all of these factors and I know that any sort of linear DC-DC is going to dissipate a LOT of wasted heat and considering the plane is made of foam excess heat is not preferred :).