I feel like that's more of an option to get after getting kullervo and his gun. Cause after that, if you ever encounter him and get the new resource after defeating him. You'll just have extra of it. I think it's a nice small source of credit farming passively. Not the most effecient, but not terrible?

Yeah you don't have to do the boosted mission as the other person said. There's a whole process to fighting sisters/liches which you should probably read up on, or watch videos on before you decide to tackle them. It's a bit confusing at first.