I would suggest having two smaller raid-groups for SATA with following raid-group size:
10 Data +2 Parity = 12
9 Data +2 Parity = 11
One hot spare per controller should be just fine.
Also by having two raid-groups in an aggregate rather than just one, has its own advantages when it comes to single whole-disk failure or double whole-disk failure. These are large capacity (1TB) drives, with slower spin rate(7200RPM) & seek time and will take considerable time in rebuilding the spare disk from parity and even more time if you are putting all the disks in a single raid-group and hence the two smaller raid group serves better.
As far as distribution is concerned, standard practice is to have all SAS on one head and all SATA on the other head.