htown1980: my cleric slinging rocks
I recall cleric makes a pretty good melee fighter too? So to me keeping him/her as a slingshot person is underutilizing him. I think a cleric can wear quite good armor, and while the weapon selection is quite limited, cleric can wield some pretty good hammer-type weapons?
Not sure about the mixed classes. Since I didn't want to have a thief-only person (but just someone who can find and disarm traps as a sidejob), I had hard time deciding whether she should be something like fighter/thief, or mage/thief. In the end I opted for the latter as it seemed I could use same allocated points for both classes quite good, but the downside was that if I had the best "thief armor" on, then she couldn't cast mage spells. And if she just had some mage robe, then she didn't necessarily have all the same stealth bonuses etc. from thief armor, and of course not as good AC either.
So in the end I ended up carrying two sets of armor for my mage/thief. Whenever I wanted to use her as a thief, she would wear the thief padded leather armor (Stuidded Leather of Armor +4: Shadowed, for example) and such, and while she was a mage, she would have some mage robe etc.
Then again, at some point I found a Robe or Armory (AC 3) for her, and that with e.g. a Cloak of Protection, a Cyclocone hat and a buckler gave her AC -5, without affecting her spell casting. And late in the game her stealth and trap detection was so good anyway that I had no real use for the puffed thief armor for those either, so I could keep her using the same armor all the time.
I kinda agree with Crosmando that having two mages might be beneficial in many encounters, but luckily you also have a half-druid. I recall druid could make some very kickass offensive area spells, like those spike spells and such which are quite comparable to the poison cloud and gas cloud spells from mages (you can, and should cast e.g. the spike spells several times to the same area, they do multiple damage then to incoming enemy hordes). I tend to use those druid area spells all the time in combat, the only bad thing about them was that when the fight was over, some of those spike spells would last quite long, meaning you had to wait a long time before proceeding (you don't want to step on your own spikes either).