hello, idk if i got your question(1) right, but i am a zfs user since about 10 years and built my infrastructure around it. But i would not use that for a single drive, as that would right from the start have zfs not being able to do, what it is excellent at: redundancy. Furthermore, zfs needs huge amounts of ram in order to run reasonably fast (and even much more of it, i you want to use deduplication).
If i use it for a single drive, i would at the very least consider setting "copies=2" to have at least some redundancy for data, i value. But zfs has advantages, i love it, and it toook only several months of getting used to it. Still: not in your case. BTW: You did not state clearly (or i missed it), what exactly is your goal you want to achieve by using zfs. It has - in short - 3 valuable purposes: It is a software RAID, a volume manager and a filesystem, all in one. If you just need a volume manager, lvm should do the trick. Since you are using an encyption layer, you might be interested to know, that zfs offers encryption since a few years too. I never used it, so cannot say anything about it.
