I do not know if going for Completionist is a big mistake, but I personally would do something differently with 18 lives/that much xp to play with. I would make the following three characters:
Elf palemaster Wizard 20. max int for elf of course: 3 wizard and 3 FVS past lives. For max spell penetration and really solid necro dcs with some enchantment too.
Human Level 20 FVS (I prefer cleric but since the forums like FVS): max wisdom for Human. 3 sorcerer and 3 wizard past lives. For really high implosion and Blade Barrior dcs and yet still solid spell penetration.
Warforge Level 20 Sorc(since 3 characters requires less xp then 18 lives on one character can fit in another life): 1 wizard and 3 sorcerer past lives. Max cha for warforge. Really great self sufficiency with awesome evocation dps.
The advantage is you can run the best character for any given quest and all are superior to the OP's completionist in one way or another which means you will always have a better character to field.
Norg Fighter12/Paladin6/Monk2, Jacquiej Cleric18/Monk1/Wiz1, Rabiez Bard16/Ranger3/Cleric1, Hangover Bard L20, Boomsticks Fighter12/Monk 6/Druid 2, Grumblegut Ranger8/Paladin6/Monk6, Rabidly Rogue L20, Furiously Rogue10/Monk6/Paladin4, Snowcones Cleric 12/Ranger 6/Monk 2, Norge Barbarian 12/FVS4/Rogue4. Guild:Prophets of The New Republic Khyber.
~Pele 24thLife~~Pezu FvS Sorceror Life 6/7~~Rhomp Barbarian! (Life 5/5)~~Llamafapper(Life 4/4)
....Can't touch this....
-Proud Founder/Leader of The Matrix-