I used to think it didn’t matter how electricity is used to generate heat, so I came to the same conclusion you did. Surprisingly, it does matter. Rather than a computer’s resistive heating, it is much more efficient to refrigerate the outdoors and point the refrigerator’s heat sink indoors. This is how a heat pump works. It’s basically awesome.

Laptops are better, because they have an integrated uninterruptible power supply, but worse because most can’t fit two hard drives internally. Less of a problem, now that most have USB3. Just run external RAID if you have to.

Arguably, a serious home server will need a UPS anyway to keep the modem and router online, but a UPS for just the NAS is still better than no UPS at all. Also, only a small UPS is needed for the modem and router. A full desktop UPS is much larger.