the max of simultaneous volume moves in 8.2 was 16. But concurrent reads (on SAS/SATA disk particularly) could impact severly your 3250. So, moving lot of volumes simultaneously can last long (more than your maintenance window).
Even if you move one by one your volume (max 16) with manual cutover, periodically, any changes made to the source volume are replicated to the destination aggregate, with possible impact on performances.
So, you should move first your volumes with the biggest workload, cut over them during maintenance window if necessary, migrate the LIFs to the 8040, and move other volumes.