My name is Plum and I am here to tell you that ~12 disk wide VDEVs are 100% fine for home use, if you're not doing database or active OS activity on there.
I don't think ZFS recommends going wider than 13-14 disks per VDEV,[Citation Needed] but you don't need to worry about getting more IO out of mechanical disks if the most you're going to be doing is file transfers and say, hash checks.