You can only figure it out through experimentation.
Try playing with what you have.
If you don't like the progression, replay the previous campaigns; they don't take much time. That might be better, although it's unclear what your Faidaen's stats are...
I spent a lot of time on "Emerald" and "Defense" – the battles were a matter of life and death, especially in Emerald, the second mission after Gilraen took a long time to complete... That's actually when I couldn't complete it, and that's when I was given a link to this forum... :rolleyes:
