Simple questions, really.

I found this answer with a similar setup, but not sure it answers my question. If it does, I'm curious why since the answer seems a bit unsure: ZFS Hard Drive Configuration in FreeNAS

I'm building a server which will be used primarily for backup, plus some media streaming, possibly with Plex. I seem to understand most everything I need, but I'm still a bit confused on how pools work, and how to configure them for my scenario.

I will have 2x 2TB WD Red drives, which I plan on using in a mirrored set up (RAID1). This would be for backup, and I'd also like to do offsite backup to my CrashPlan account from this array. I also have a few other drives: 1.5TB, 320GB, 250GB. I'm not sure exactly what to do with them yet, but looking for options. FreeNAS OS will be running from a 16GB USB Flash drive.

• Would it be wise to use the 1.5TB as a backup-backup, essentially as a mirror or perhaps for snapshots of the 2TB RAID1? I'm still learning about snapshots.
• Should the 2TB mirrored drives be in their own pool?
• Should the other drives be set up in their own pools as well, or should they be JBOD in a single pool? They may or may not get much use since the 2TB array is plenty for me.
• Does a dataset basically mimic the idea of a partition or a network share? In other words, I would map \SERVER\Share to X: on my laptop?
• Let's say I wanted to use the 250GB drive as an encrypted drive to store all of my cat pictures. Would it have to be in its own pool?
• If I use jails apps, should they go in the backup RAID1, or in another place?

Thank you!