Well look I was level 22 when I started it. Make sure you have your immortals learn level 2 spirit magic. This enables them to cast GAMBLE. This is by far one of the best spells in the game at this point and a few of us even think it might be broken. It seems to do in the upwards of 1000 damage when it hits good but the thing is, it hits good often. If you don't have gamble, get it from the little girl in the Tosca village. The one with the statue mini game. You have to find all the statues. (its not to hard)
Also make sure you can cast seal. You will want to seal the bigger creatures so they don't do any magic. The ground pound is the worst but you should be able to have some characters survive. I had Kaim, Seth in the front, Ming, Mack, and Janseen in the back. Everyone casted Gamble (this works well on the silver guys too if they don't flee and you get 8 sp for one kill and level up as well) and Jansen needs to cast Seal and then Poison.
I got to level 40 with Kaim ( the other were in the high 30's) and then decided to continue in the story but my friend said it will let you get to 49 and then the level cap kicks in.
I posted a video on my you tube about it. Should be the first main video (sorry I can't link the video url, I'm blocked at work.)
www.youtube.com/slasherthrasher