The thing we have to remember is that, although orb income won't be huge, there will be a consistent income of orbs outside of missions. We get daily rewards for simply opening the app each day, though I don't think all the rewards are orbs.
You don't want to pull for new characters each and every day, especially when in the future, there will most likely be better banners advertising new and better characters. I'm probably going to do one more 20 orb pull, and then I'm saving up until Ike and the crew get here. So instead, focus on leveling any character you can.
If this game is anything like FFRK (which so far, it has a lot in common in terms of missions), we will get more story missions and very soon, event missions, which will probably give us more orbs.