With regards to Southern Air,
Per our Flight Operations Manual, any potential captain must have:
(1) 2,500 hours of total time on a turbojet aircraft of more than 41,000 pounds max take-off weight
and
1,000 hours of PIC time in a turbojet aircraft of more than 41,000 pounds max take-off weight
OR
(2) 1,500 hour of SIC time in a turbojet aircraft of more than 41,000 pounds max take-off weight and 500 hours as SIC with the company.
If Southern is your first part 121 job, there is absolutely no way that you will upgrade to PIC in 2 years. My understanding is that they average about 300 hours per year, which would be about a 5 year upgrade.
Also, remember that as an FO at Southern on the 737, you will see no change in pay until year 4.
Expect to make minimum pay. I have only credited more than minimum pay at Atlas (same CBA as Southern now, essentially) 2 months so far this year.
That would mean that you should expect to make $80x61x12 or $58,560 for your first three years.