I would say if you want the optimal party you're looking at:
Minotaur/Lizardman/Human/Ratling Barb Heavy Weapons: Each of these choices has different pros and cons so choose the one you like the most.
Minotaur(Only choose 1 Mino)/Lizardman/Human/Ratling Barb Light Weapons: Eventually aim for dual wield for maximum damage.
Lizardman(probably worse than Ratling/Human)/Ratling/Human Rogue: Either dual daggers or missile weapon spec is probably viable and end game using both is probably best.
Ratling/Human/Insectoid(probably worse than Ratling/Human) Alchemist(mage): Level in order, getting 1 for each to begin with then either going to 4/maxing alchemy or putting fire to 3 then maxing alchemy, Alchemy(1 level initially), concentration (up to 3), fire (up to 3 or 5), air (up to 3 or 4, only 1 until water to 3), water (don't level this until 4/5 alchemy, 2/3 concentration, 3 fire, 1 air, but then level to 3), do not level Earth (poison spells are mediocre, and by the time Ice Shards is worthwhile its outscaled by Frost Bolt).
I think Alchemist Mage build is better than going for a Battlemage since Alchemist is only really worse than Battlemage as a backliner in the early game where the Alchemist can't cast until they get a wand/orb, but there are Wands/Orbs early in the next couple levels. Further, using an alchemist as a missile weapon user is categorically worse than a rogue missile weapon user, while the actual difference between battlemage and alchemist as magic user ends up fairly minor (battlemage has slightly more energy and can cast without an orb/wand) especially compared to the difference between Rogue missile weapons versus Alchemist missile weapons at high levels (at level 15 rogue gets 15% more crit chance with missile weapons compared to alchemist which is equivalent to 5 points in Critical). Also late game you can spam bear potions (which may have higher dps than magic in the end game, although I've only heard this not tested it)
Without Alchemy you lose out on a lot of possible damage from Energy/Rage/Bear/Speed (I think you can brew these) Potions, Frost/Fire/Lightning Bombs. Healing/mitigation from healing/shield/necromancer potions. Also quite a significant amount of stats from brewing attribute potions.