I would recommend option #1 and strongly recommend against option #2 (the voltage coming across a USB port is going to fluctuate a lot more than what comes directly out of a PSU, and you then also become susceptible to any kind of chipset oddities where the chipset ends up ceasing flow of power to the +5V line -- some do control this! It's not a blind passthrough!).
Me personally, I'd go with option #3 -- if you're building this NAS, then get yourself a PSU that has native SATA power connectors on it (no need for Molex adapters -- I hate those things anyway).
Or alternately, get yourself a decent NAS chassis that has a hot-swap backplane in it so the drives are natively connected via SATA; many of these backplanes have one or two 4-pin Molex connectors on them.
The Seasonic PSU linked earlier includes native SATA power cabling for up to 4 drives, from what I can tell. If you went with 5 drives you would need to use one Molex adapter.
Footnote: I will warn you in advice: port multipliers have a whole series of bizarre behaviours, many of which are driver-level. The exact SATA chip being used with PMP plays a huge role here. I can point you to real-world fixes for these type of things in server-class OSes (ex. FreeBSD) if you think I'm kidding. The general recommendation is: try to avoid PMP if at all possible. This isn't even touching on the bandwidth/performance aspect of PMP (4 drives being accessed will certainly saturate a SATA300 port, and very possibly a SATA600 port).--
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.