Your choices were knight, monk, sorcerer, and cleric, so you picked the two strongest fighters and the two strongest spell-casters. I think you should try paladin, archer, thief, and druid. The paladin and thief will be your primary fighters, and the archer and druid your spell-casters. Note that when you play Light, only the thief can have even master level disarm traps. If not for this, I'd say pick a ranger as the fourth character instead of a thief. Rangers are very diverse, capable of getting expert level with elemental and self spells. This may not sound like much, but there are some things to choose that can make them excel. Let me tell you what I think...
Give the paladin mace and shield, both of which he can grand-master in. You want someone in the group to be able to take hits, like a knight or monk could, and also have a high AC. Otherwise, you can give the paladin mace and sword, for more damage and accuracy. The paladin's ability to paralyze with his mace at grandmastery is unequalled in the game. Get the skill as high as you can and it will pay off. Note that none of these characters has the kind of high hit points of a knight or monk, so having someone with a very high AC can save you if everyone else goes down and AC will be more important to everyone for the same reason.
The archer should use a spear in both hands for his melee weapon, and don't bother getting mastey with it because you won't use anything in your off-hand and in melee you will also have spells to choose from. The bow can excel because at mastery you get two shots and then at grand-mastery you add the skill rank to the damage of each shot.
The thief should learn sword and dagger, and use one in each hand. I'd say use two daggers always, especially in the later game, even though there are some really cool swords in the game. You can grand-master daggers, which gives you a bonus to damage equal to your skill rank, and if you get it high enough you will often do triple damage. You asked how to avoid needing a cleric for the cube bosses? The best other way is with a thief, who can STEAL their control cubes right off them! You have to get the skill very high in rank, though, but with few other skill requirements, you should have all the ranks you need. -Just keep raising stealing as high as it can go.
The druid should use a staff. He has more spell-points than any other class, with grand-master meditation. You can master all the elemental and self spells. Give the paladin and the archer each one or two magic skills to develop, so the druid can get high in the ones you think you'll use most. You may want skill ranks for alchemy, too.
If you pick a ranger instead of a thief, you'll need to rely on telekinesis to open treasure chests a lot, and the ranger should get his axe skill very high. There is an axe which increases the user's earth magic skill which you can get, so with this, the ranger can be great to pick up expert earth magic and develop the skill rank high for stoneskin, and offensive spells like deadly swarm and blades. His archery will be good, too, with two shots when he gets mastery.
My favorite is the Knight or Monk, Ranger, Cleric and e Sorcerer. I use the sorcerer mostly because I love the LLoyds Beacon spell, it affords instantaneous travel, plus invisibility and flying. Its a great light party, and the ranger's first promotion quest is the easiest in the game.