Somehow I got lost on the math there DC. 1.28 * 1.28 = 1.6384, divide by 4 and you get .4096.
How do you come up with .5 watt?
He will need 8 mosfets, each one will run 1/8th of the time (12.5%), each one will need to be able to source between 0 and 1.28A. I see the 1.28 in there, and the 4 was from half watt times 8. So I see some of the numbers, and understand where they came from, Im still confused with the math, and where half a watt came from. it seems arbitrary.
I tried crossroads technique, and came up with 7 P-channels, I started by searching "p-channel mosfet", then clicked a link that said Fets-Single, That displayed a page with many options, I selected logic level gate, through-hole, and then I scrolled the package column, and selected the TO-220-3
From there, I notice that all of the parts have many mOhm RDS (way way over .4 ohm), not even close to mOhms.
I dont know what a good/bad gate capacitance is, but I can only find gate charge, and input capacitance.
I can also see that the NDP6020 is rated at 60 watts, and if using 1/2 watt, Im guessing you wouldnt need a heatsink.
How many 20mA LEDs could you run on that mosfet?
Also $150 for the parts for a 8x8x8 cube sounds like a lot, but I havnt built a cube that big.
6 Meters of wire seems like a low estimate to me too, I bet you use over 8. what kind of wire is it? soft wire is very difficult, but harder wire is a bit easier, and ends ups being sturdier. I find very hard steel works the best. For cube building, and general keeping wires straight, thinner and softer are more difficult, thicker and harder are easier, but for soldering, thinner is easier.