Re: memory requirements?
"I thought the big problem with ZFS was its vast memory requirement? 1MB of cache for every GB of disk or something.."
1GB of RAM per TB of disc is the rule of thumb you were thinking. However, see http://www.solarisinternals.com/wiki/index.php/ZFS_Best_Practices_Guide which simply states that 1GB or more is recommended.
The idea of having a decent sized RAM cache is not unique to ZFS but recommended for *all* file systems.