No, the Qreplica feature only works via iSCSI communcations between two QSAN SAN systems. 
No, the Qreplica task operation follow a one-to-one rule, which means once a virtual disk is assigned with a replication tasks, it cannot be assigned the second replication task. Similary on the target end if a backup type virtual disk has been assigned as a target of a replication task, it cannot be assigned again as the target of another replication task. 
No, as the replication job works at block level, once interrupted, the replication would have to restart again.
With the latest Qreplica 2.0, there is no spec limitation in the replication speed between two Qsan SAN systems. In theory the replication speed would be able to reach as fast as the effective bandwidth of the network path between the two iSCSi ports. If the traffic is routed, overheads brought by routing actions should also be considered.
The bottom is used for restoring a tranformed local clone job to a remote replication job in Qreplica. This is often used when you need to clone a set of VDs locally and then have the RG roamed a remote replication, to eliminate the long time needed for running the first time QReplica full copy via a slow external LAN or WAN link. For details about how to use this function please consult Qsan techical support team. 
With the latest Qreplica 2.0 you may create up to 16 or 32 replication tasks, varies by model. 
The following requirements need to be met before running Qreplica between two Qsan SAN systems:
1. Both systems need to have Qreplica license installed and activated. (For all Qsan brand SAN models with Qreplica feature, the feature is activated prior to shipping).
2. On the target end, the RG and the target VD is pre-created and the effective size of the target VD has to equal or greater than the source VD.
3. The VD type of the target VD has to be adjusted to backup-target, while the VD type of the source VD is configured as RAID type.
4. The path and IP configurations of the iSCSI ports on the two systems has to be properly configured to ensure that the iSCSI commucation works properly.
The Qreplica feature is a block level replication mechaism that works between two Qsan SAN systems to effectively replicate the content of a whole virtual disk. The Qreplica works in a snapshot based manner so that everytime a replication is triggered, a snapshot on the source virtual disk is taken and the replication will then replicates the contents of the source virtual disk based on the snapshot status, to a pre-setup target volume on the remote target end.
No, once configured on creation, the property cannot be changed anymore. You will need to re-create the VD if you wish to change this property. 
Depends on how much data you store in a volume with fast rebuild enabled, the more empty the volume is, the faster the rebuilding speed is. If the volume is fully occupied then the fast rebuild does not bring any improvement in rebuilding time.