Well beth one thing you will find in order to have cop success your going to have to level up some of your other jobs. I started gathering folk for 5-3 and i'm now on 8-4, and one thing held true i was a different job for almost all of them. It happens do to you never know who or what jobs your other runners will have. I'd say your going to at least have a minimum of two jobs you can bring that will be useful through out your missions. Yes it will take time but it is well worth it to get there trust me sea is cool, and a change of pace.
I leveled tank, dd, and mage jobs not for the missions but allready had them so it helped. I have heard others who will actually level just for these missions, so in closing imo you just need to bring more ammo to the fight. But i wish you luck as it's a long road but well worth it.