I'm using a Pico PSU (60W model IIRC) on an Intel Core I3 4130T, Intel 128GB SSD, 16GB DDR3, 2 TB drive and Asus motherboard. Pulls 19 Watts at the wall most of the time but spikes occasionally.I wouldn't use that platform, I would get one of the newest Intel chips that have a GPU that can decode HEVC. You might as well build something that will be relevant for more than a year or two. This build would have been great in say 2014 but the world has moved on.
A Pico PSU can be fine as long as you stay under 50% of its limit. You need something like a KillaWatt to make sure.
The only way I know to go completely fanless is to get one of those cases that is a heatsink. Like these:
Maybe you're thinking of the motherboards that have a direct connection to a power brick. Regardless, the picoPSU uses a power brick. Just plugs into the ATX power connector and has an extension that runs to the back of the case (where the brick power supply plugs in similar to a laptop). Out of the picoPSU are several cables for power.I don't think we're talking about the same thing. The build I linked is using a power brick like you'd use for a laptop, and no picoPSU.
I think it depends on what OS the op is using. If he is running something like Unraid which loads from a USB there is no need for an SSD.To reply to your questions, according to Amazon reviews it powers SATA drives through the motherboard. One thing I disagree with is the SSD. SSDs might be necessary if you want to speed up a sluggish laptop, but since this is a desktop and since you're getting a $100 4TB disk drive already, is the SSD even necessary?
If you are truly frugal and looking to save money I'd strongly suggest purchasing a used Dell or HP SFF off EBay which will give you equal or higher performance at a fraction of the cost. I'm talking $80-120 for a fully built system running Windows.