its the gathering portion that sucks
your supply line is where you are going to be ripped off the most for profits, as there are specific quests and recipes in general that require really inflated materials. To circumvent that, you will want at least one gatherer at 45. On each world, the economies are different, and every week, peek items of value change. What doesn't change is the need for gatherers and the need for frequently used base materials.
finished lumber, ingots, thread, and undyed cloth are a fast way to break your first million.
Lumber and thread will depend heavily on botanist, ingots on miner.
The idea that you have to hit 50 in all classes to make money is false. You can generally make money around level 25-35. To break that coveted 100 million mark though, I dunno, I never did, and I think you need 4 star crafting, which will require alot more than just 50 in 11 classes. like 30 million+ in gear and materia melds.