I don't normally announce such trivial accomplishments, but, well, it is my first time playing Wizardry (any) and, well, while not exactly noteworthy, it isn't exactly trivial either.

My party is as follows

Gender Race StartClass ClassChangePlan
Female Faerie Priest->Bard
Male Dwarf Psionic->Ninja->Samurai
Male Elf Bard->Lord
Female Mook Mage->Monk->Valkyrie
Female Rawulf Mage->Ninja->Valkyrie
Female Felpurr Alchemist->Bishop (then maybe Bard if I make my Faerie something else)

I plan to do all of my class changes around level 11 or so, except I'll time my changes so I always have at least one bard. I get the impression that since we all save after each event more significant than a move, party selection really doesn't matter, but if anyone has anything to say about my merry band, I'll happily read it.

The very beginning of the game can be pretty frustrating because your characters are so fragile. Once you make it to level 2, it gets a lot easier to make progress.

Don't fret too much about your party build. It's a lot of fun to play around with all the different skills and classes, but as long as your group is reasonably balanced, you should do fine. I beat the game my first time through with a very basic party. Level 11 might be a long ways to go with no front-line fighters, though.

Once they reach lvl 11 the game is almost over. If you are to change class in Wiz 6 it's better to do it at lower levels.
In the end game low level characters will hurt, since character level determines chances of resisting enemies' spells and special attacks. And low level characters attacks, spells and abilities like hiding and critical hits will fail more often against high level enemies.

Things are different in Wiz 7 where you really need to class change several times to get enough skill points, but in Wiz 6 that's not a problem.

A balanced party without class switching would have a considerably easier time than yours, it would be considerably superior to yours at each XP value during the game until the end. Nothing additional grinding can't solve though.

That was certainly not my experience.
You get fewer skill points to distribute freely (having to spend points on Weapons skills is annoying, since these skill increase rapidly through use), so it takes much longer to be able to cast high level spells, for example. Cure Poison is a relatively high level spell, but you encounter enemies with poison attacks long before being able to cast the spell. Same, but smaller problem with Disease.

In W7 a priest (applies to mage, alchemist, psionic too) with 12 int&pie gets as many academic skillpoints per level up as total skillpoints in W6. Considering that you get even more skillpoints at level up in W7 as your stats increase and reach higher levels you gain access to the higher level spells in earlier parts of the game compared to W6.

The W7 priest can expect to get access to level 4 spells like cure poison at character level 7 and to reach the highest spell level at character level 13, long before the end.