The 501 and the 503 come back to ABZ to operate the 507 and 509 I think and the 505 stays up there for a while not 100% sure though
100% correct. The 505 comes back to operate the 513.
The issues with payload are when the runway in SCS is wet and there is little headwind. This mainly effects R06. In these cases they usually operate all 4 aircraft. Not usually a payload problem leaving SCS.