[Too Darkpark]

so far so good, but seem to be stuck on rank 7 of the battle square. hmm...
so far i've been using my fighter(4)/barbarian(8) to fight all the monsters and before taking on a level i'd buff him up with some sort of strenght boosting spell, stoneskin or ironskin, and finally improved invisibility. this has been very effective for me, but i'm at rank 7 and the monsters are very tough. here are some of my concerns:

1) should i switch off to a different character eg: one with a bit more magical power like a cleric?

2) should i continue using the above character but wait til he goes up another level or 2?

3) try some different tactics? other buffing spells that i'm overlooking?

4) besides some $$ and XP are there any good magic items to gain by progressing to rank 10?

thank you.