Yup, 12 total per week and no more then 6 per source. So you can either fully supply 2 of the girls each week(so far theyre all girls, the next custom deliveries client hasnt been announced yet) or you can partially supply all 3. Kurenai pays the best overall(Zhloe and M'naago pay the same amount since a recent patch, but a Zhloe or M'naago on bonus pays more then a normal week Kurenai), so leveling her rank up is a good play. If Zhloe is at the highest rank already you could do both of the other girls on weeks that Zhloe isnt offering the bonus(with bonus zhloe plus either of the others on the weeks she does have said bonus). Or you could talk to both of the new ones and decide whos cause is more important to you and help them first. Either way, its free scrips if you do it right(if you get the collectable to the highest level on the first try then the gil you are paid is more then the cost of materials - not sure how the math breaks down at lower collectable ratings or with crafting botches).