The FAS3140 has an aggregate limit of 75TiB in 8.1.x
The maximum (optimal) RAID config, according to the "Storage Subsystem Technical FAQ", is 2 RAID groups with 17 drives each.
That would leave you with 1 aggregate with 34 disks in two RAID groups and 1 aggregate with 12 disks in 1 RAID group (leaving 2 spares)
That's probably what I would go with, except if you want (almost) equal space for each of the two aggregates, in which case your Idea (22 Disks for aggr1 and 24 disks for aggr2) looks good, although you'll loss a few TiB in total because of the two additional Parity/DParity drives for the fourth RAID group
-Michael