If it's ventures, it's usually encouraged to have an even number of DoL and DoW/M classes, like for example, I have 5 of my retainers as classes of DoW/M and the other 5 DoL. You also want to send them out on the 18 hour ventures as those are the ones that could bring back very valuable things like the stone partitions and neon lights. Otherwise, my retainers bring me almost 100k worth of Allagan Gold Pieces daily. The mats they bring back, sell them on the MB to make some more Gil or use them to craft things to sell on the MB. Make sure to equip your DoW/M classes with the highest ilv gear since that affects the things they bring back and for DoL classes, make sure they also have the latest gear possible for the same effect. Melding materia for DoW/M classes is not needed but melding Perception to the DoL classes does affect the number of things they bring back, so meld as much Perception materia on all of your DoL class gears. Also, it's ideal to have an even number of DoL classes too, like for example, I have two of my retainers as Botanist, two as Miners and one as a Fisher to sell the mats they bring back from their respective classes. DoW/M classes all bring back from the same loot table.
You can also sell things like crafted gear, food and medicine to make a steady income too.