FWIW I did delay the main game in DKK for exactly that reason when playing with my K,C/T,R/C,R/C,WM,RM party--wanted to build up some levels so I could turn away all the wights. I actually played the game straight through the first time and had a really hard time in the Clerist's Tower.
Go ahead and toss your Cleric/Thief, but I'm not sure a C/F/M is your best choice--they'll really start falling behind in levels in DQK.
By prior posts, your party stands at:
1x Human Knight
1x Qualinesti? Fighter/Red Mage/Thief
1x Human Red Mage
1x Kender Cleric(Kiri-Jolith)/Thief
1x Qualinesti Fighter/White Mage
1x Qualinesti Fighter/Cleric (Majere)
Giving the kender the boot, you have four characters who can fight, three mages (though Jack of All Trades is going to start falling behind in Dark Queen), a thief, and one lousy cleric. My first thought is Qualinesti Ranger/Cleric--probably Mishakal for the healing bonus, cause a ranger will be handy against the fire giants in the tower. If you're fireball-happy you can go with a Qualinesti Cleric/Mage instead.