isi_vol_copy_vnx with celerra VDM that has file system

We would like to have a migration from a celerra to an Isilon using isi_vol_copy_vnx. I wanted to ask if there are some best practice rules that should be followed according to your experiences if you've tried it several times and you've faced certain issues.

-          For example, is it ok to use the interface used on the Celerra for the File system  for the migration or would that affect its performance as it’s in production? As for the Isilon side, how much bandwidth would that use up as well and is it going to use both ports from the node doing the isi_vol_copy_vnx command?

-          If there are for example 3 different 1 TB files to be migrated, is it best to run 1 isi_vol_copy at a time or can we run multiple instances of them and how to check their progress on the background?

-          Also when it comes to defining the NDMP user on the celerra to be used in Isilon migration, is it only enough to have it on server_2 on Celerra ? The file systems on the celerra are on Virtual Data movers, I was trying to migrate on a lab using same equipment, it worked for physical but not for virtual VDM, so is there  a certain trick behind it to make it function?

Appreciate as much details as possible.

Thanks a lot!