I became a FO on the 742F at 21 and left at 25. Without doubt, this was the best time of my life. Pay was significantly less (for me at least) than an equivalent colleague on the passenger side.
The pilots I flew with were the most down-to-earth guys I'd ever flown with. I don't want to seem like I'm putting anyone down (on the air-freight side or road-freight side) but the banter that went on was just like the banter you'd see between a group of lorry-drivers sitting in a greasy spoon.
Excellent personalities and great times in weird and wonderful places away from the tourist trap locations. Very unsociable hours but you get a lot of time off. My average was about 450 hours per year so quite a lot less than pax pilots. Luckily, I had already become un-frozen after flying 732s in the Philippines.. So keep that in mind - especially if you are starting out in a 74X-F.
The cargo industry is taking a hammering and it may take you 3 years before you become unfrozen with 400-500 hours a year.
My advice is to think very very carefully about paying for the TR on a 74X-F. Don't be blinded by the status of being a "Jumbo-Jet" pilot straight after training. I know it's hard but being a start-up airline and being asked to pay for a rating definitely sends alarm bells ringing in my ears.
On one hand, moving to the 744 is my biggest regret. The flying is without doubt the most boring I have ever done. I would gladly move back to the 742F tomorrow with a significant pay reduction. On the other hand, the stability (lack-off) is frightening.