hey Sam,
did you get any further with this? In general I’d not use a separate zpool per disk as this obviously limits the overall iops of the system, and would make it difficult to get benefits out of a zil or slog.
BTW there’s a FreeBSD foundationdb-devel port now that might be of interest to you, and as soon as FDB 6.3.0 lands (which has cmake for proper C binding support) the main databases/foundationdb one will be updated too.