Please ADD FUSES. Resettable polyfuse (preferably on lines going from atx supply directly, before your electronics) will save you a lot of trouble if something goes wrong
ATX power supplies can supply a LOT of amps and even tho they generally are over-current protected.
Like even 250W one can usually put ~20A on 5V line and often more than 10-20A on 12V, which means if you fuck something up you can even evaporate some component or trace on target device before ATX limits even trigger.
While fuse is not an 100% sure protection (it has delay, so there will still be a power spike, power regulator with current limit will be much faster than fuse), it helps to at least limit the damage