ZFS metadata structure works in a much more complicated manner than that of other file systems such as ext4. Modifying any part of the data structure involves actions of updating relative checksums and metadata all the way up to the root layer and the ZFS uberblocks. This becomes most obvious when the operation containts lots of write/modify/delete actions to large amount of small files.
With mutiple copy (more than 1) configured for a zfs, the write performance will be reduced by more than 50% (two copies) or more than 67% (3 copies). No obvious impact on read performance can be observed. 
The "number of copies" options offers the possibility of keeping up to two more "shadow copies" of data stored in every single block. Using 3 copies in this option would therefore occupy 3 times capacity for storing the same amount of user data. 
No, thin-provisioning only has effect on space allocation of zfs. Enabling thin-provisioning or not does not have any impact on peformance.
On a Qsan NAS a volume with thin-provisioning enabled, the size option of the volume does NOT grey out like a thin-provisioned file system. This is because for a SAN volume presented to a host, a fixed volume size information is always required and cannot be changing dynamically. 
For a file system with thin-provisioning enabled, the quota and reservation space of the file system from the pool no longer exists. User may notice the file system size option greys out while configuring the file system property or creating a new file system. The thin-provisioning option can be enabled and disabled anytime after a file system is created. 
Thin-provisioning provides great flexibility in free space management, which allows the user to create a file-system with dynamic quota or a volume with capacity prevision possbility.
The data written before the new RAID set is added will be kept in orginal place. Any data modified or written in after the new RAID set is added will be distributed evenly (handled by ZFS algorithm) into the RAID sets based on the portion of free space available from each.
In theory there is no limitation on the number of pools you're allowed to create on a Qsan NAS. However since each pool must contain at least one disk, so the maximum number of pools allowed is equal to the maximum numbers of disks allowed on the system.
By ZFS design, you may only expand the pool capacity by adding additional "RAID sets" in the pool. Browse to the pool options and select "expand" to select free disks for creating an additional RAID set in the pool to expand the pool space.
You cannot expand the existing RAID set in a pool to include more member disks nor migrate the RAID set to a different RAID level.