Yes, you may create a pool using disks across the JBOD but it is suggested that each RAIDset inside a pool only resides in a single chassis. 
By doing a scrub the pool automatically checks through the ZFS tree structure and verifies all the checksums. You may do this periodically to ensure that the file-integrity is in good status, though the ZFS would also checks the data integrity while the data blocks are being accessed.
No, if a disk belongs to a pool that's been imported an online, the disk cannot be forced free. The disk types allowed for setting free are spare disks and disks in reserved status.
When an encrypted pool is created, a private key for decrypting the pool is automatically generated and stored in the system. When the pool has to be removed and installed on another zfs based Qsan NAS system, upon installation and importing the pool.
A UserHome directory on a Qsan NAS is used for:
1. Storing private share space for local user accounts:
Every local account created on the Qsan NAS will be automatically assigned a private folder under the UserHome directory, and shared automatically (restricted to the user's private access only, exclued Administrator access).
2. Storing necessary system debug information to be used as a important referecne for Qsan engineers' debuggin purpose, if required.
It is therefore always suggested to have the UserHome directory assigned to one of the pool in the system. Once assigned, the UserHome directory cannot be removed or re-assigned, unless the pool with UserHome directory is destroyed/removed from the system.
No, on a ZFS based Qsan NAS there's no initialization action required for a new created pool or zfs before it's ready to use.
Since a pool is consisted of at least one physical disk, the maximum pools you may create on a system is therefore equal to the maximum number of disks you can create on the system.
For zfs (volumes and file-systems) there's no limitation on the amount of creation. 
If the disk had been used on other storage systems prior to installation on the Qsan NAS, upon installation the disk may appear to be in "reserved" status.
If a disk belongs to a incomplete new pool that the Qsan NAS ZFS fails to import upon system startup, it may also appear as "reserved".
Theoratically for ZFS there's no limitation in the number of disks that can be installed on a single system. However due to hardware design limitation the maximum number of disks allowed on a Qsan NAS products is still limited. 
A pool is consisted of disks of one or more RAID sets. The zfs (volume and file-systems) are created on top of the pools, extracitng space from the pool for storing data.