I'd wager much more people are doing ZFS + external drives than many people think -- it's very convenient and that trumps recommendations, it seems.
I am aiming to have a proper server OneDay™ and will make sure I get one with enough PCIe lanes so I can have several slots for 4-6 HDDs or SATA SSDs but in the meantime a simple thin client + a professional external HDD has been getting the job done amazingly well.