I have to agree with Grim, it's a good idea to take the extra precaution.
If you do happen to want to put in some extra fans without power worries, you can always just get a cheap external computer hard drive enclosure:
example of cheap enclosure (not meant as a sales pitch)
You basically just ignore the "enclosure" part ---use the wiring & external power supply for 12v power.
You can use it as a "quick & dirty" solution --just drill a hole for the wire.
or
Really go all the way, cut a hole in the 360's back or one of the sides ---into which you can glue or
mount the "face plate" from the enclosure, for external access to it's plug & power switch. ----Or,
remove everything
you need from the enclosure "face plate," and mount it directly through the 360
exterior.
Personally, I'm using the "quick & dirty" solution, while I work on my full-on mod. I'm using squirrel cage blower "fans" anyway (for the time being), so there's no easy & attractive way to do my set-up. Mine should be a falcon --I haven't checked, because I've got a couple weeks under warranty, to go.
You have to check your amperages, to see how many fans you can run off the set-up, but if you over load it, at least your 360 is not disabled.