Sounds like GSS is a job for those who cannot find another job (i.e., lost a job and cannot find one due to the economy) - or they are just fans of the 747 who are also gluttons for punishment. Given that GSS has such a poor repuation for terms/culture/morale, I cannot understand why anyone would consider staying LONGER than the training bond requirement. Just get your 747-800 experience, see the world (check the destination boxes with some serious fatigue) and then find a better job with a marketable 747 type rating...
Go in with the right attitude and the expectation that you will leave down the road. You will then feel a lot less stressed...
From what I have heard, don't expect to go to GSS and then change it much for the better. Why try to push a river uphill? Unfortunately, sounds like that culture focuses on cheapness and low margin freight flying. Sadly, this is the state of many airlines around the world where pilots are not considered professionals who deserve competitive wages.
Quite a shame that GSS is really this bad according to the many voices on this and other forums - it has the potential to be a great job with interesting/varied flying and excellent equipment. Too bad pilots are given no respect in this case (although quite common these days).
Pilots qualified to fly the 747-800F should not have to worry so much about paying their basic mortgages (or divorce alimony combined with mortgages given these rosters).
So, to reiterate, I wouldn't go there and expect to make any money. Just try to set your expectations accordingly. Instead, go in like a mercinary and get your type rating, get some good international flight experience and hours, and then find a better job. Stay until you can find a better job (maybe look at the ME or Asia for starters as your training bond is almost paid off) and then leave it behind.
Change your attitude/perspective and treat it like the temporary job it should be! Pilots = mercinaries these days.