Welcome to the boards, eddie-c! May the dust you blow off the game be the decaying bodies of your enemies...
You've got good advice from the man, Radek. 7th-level spells are only available to a native caster of that school, or to an enlightened zenmaster. And you don't get one of those to the end of the game
For advancement, check the Best Tips thread for more ideas. I try to change fighters ASAP and leave spellcasters until they get their level 7 spells. Rogues... I don't even play. Why bother?
But by the time you get one to Ishad N'ha, he or she will be very ripe for a class change.
And like Wyv said, the best thing about this game is that there are no wrong answers. Everything is an option, and the only impact is different effects in your game.