I don't think it will be a problem. It's an M2-ATX, so it's good to 160W.

Let's look at what it has to power though, and what actually is powered by USB:

*monitor? Nope - has a separate 12v power connector for the car's battery power;
*wireless keyboard and mouse? Nope, just the transmitter needs to be powered - the mouse and keyboard have AA and AAA batteries for power;
*optical drive? eh, yes and no. The USB won't provide power, but the optical drive is being connected to the PSU. I am making a custom harness specifically for the optical drive because it'll be so far away from the mobo/PSU;
*portable storage? not much power needed there, if it's used.
*GPS Module? Yeah I'm sure that uses some power, but not THAT much!
*Others (bluetooth; wifi; ??) I can't think of too many other things that would use a lot of power. The power supply is 160w and it's barely going to be supporting anything major; I'm confident that the PSU I have is way more than I need!