Small compact party:
Sorceror MUST have, go to stratagy section read all about them especially solo as they explain the RIGHT SPELLS for all mages Sorceror or otherwise.
Berserker and/or Undead Hunter as both are immune to level drain with fighter thac0 and can be hasted/improv hasted. A monk if you give power amulet too.
Gnome thief/illusionist [staff of magi invis while detecting traps, cloak of non-detection] scout superstar
Straight Cleric with Crom Flayer hammer and mass AC shield and best Armor. With correct spells you are, BAD, sanctuary and heal tank, Neg plane protection and restoration. Later raise undead especially when cleric hits lvl 16, as raise undead warrior, nasty these. Gate and protection from evil.
All spellcasters require stratagies you need to have planned out before you ever run into that type of monster.
Example: Everything can be held by web, except spiders, and people with ring of free action on, cast web summon spiders. Undead are very suseptable to web, but a lot of vamps are immune to spider damage, Berserker with ring of free action.
DO NOT SAVE spells. Every battle is your last. The computer plays that way with its characters, so should you.
DO NOT BUILD the ultimate HERO. Build the ULTIMATE TEAM. Think how everyone works together.
Scouts allow you to prepare for the enemy. That is why a multi-class not dual class thief/mage is the best scout. You can cast true seeing and stay invis/hidden. While invis you can detect and disarm traps and open doors. With the cloak of non-detection only those creatures immune to invisibility can see you and those are few. Scouts also lay traps. Let your Beserker pull the enemy into your traps etc. When raged he is immune to all mind effects. The thief sets up the ambush and waits. Someone else is designed to be the bait.
Mages kill mass low level enemies that can overwhelm. Mages remove spell protections so the fighter type can kill the other mage. Never use your mage to try and kill another mage. Use your mage to allow your fighter to quickly kill him. Mages are the true assassins of big nasty fighters. Greater Malison, cromatic orb and later Horrid wilting. Cromatic orb KILLS on a failed save at high levels. Spook only lasts 3 rounds, but is -6 to save at medium high level mages. Greater Malison makes that -10 to save.
Clerics make them your high AC tanks. There spells take longer to cast, the reason for armor and shield. Sanctuary and heal at lower levels, when things are tuff. The only real usefull lvl3? spell is hold person, fill almost all your slots up with that spell. Mage Greater Malison on crowd then hold person equals nice results. lvl5? Raise Dead, like mage at lvl 15or16 you raise skel warrior. Mages need other spells besides true seeing at lvl7? Your cleric is the best to memorize that spell. HARM has no saving throw and reduces a living apponent to ONE hit point. Protection from evil/prot evil 10' and gate. If party is good alignment, holy smite is an area effect evil only damage spell. MOST of your enemies are evil. Is a less effective version of Horrid Wilting used this way. TURN undead, most undead are immune to most things, but this. Clerics hit high level fast and get lvl7 spells not only soon, but many. High WIS means more spells.
Berserkers, ultimate upfront tank. Can specialize as high as you want. Dual wield. For 10 rounds are immune to everything, but damageing spells. AC drops 2 points more. Great tanks, their simple and very effective.
Enough info for now