SATA power connector usage
It's totally ok to wire all pins of the same voltage in parallel. That's how they're wired inside the connector anyway, so don't worry about it. The power disable pin is not used often on standard ATX power supplies, so don't worry about it unless you're plugging you device into some server appliance that might have a backplane that uses the power disable pin. Big server drive sleds use this pin, but standard PSUs don't. Same goes for staggered spinup, if you're connecting your device to a standard ATX power supply, just treat it like a GND and wire all the GNDs in parallel.