Crews get paid for EVERYDAY they are out on contract. Whether you are on a day off, sick, flying , travelling, or hung over..you're still getting paid. They do not pay you when THEY fly you home at their expense on vacation.
Typically most guys will for 4-6 weeks and go home for a couple. It varies.
RE:B747-400 Capts. Not sure I fly the Classic. I think they make around $350 USD a day so that is $10,500 on a 30 day month + the $1500 perdeim. $12,000. That's completly tax free paid offshore.