Honestly there's no reason to leave Kurn's until 24+. One of the best exp mods in the game and close to home, which will be a rarity for you moving forward. Maybe you need to head out to get some spells that can't be found in Cab once in a while, but other than that Kurn's is perfect.
The only upside I see to Warrens is working Heretics faction so you can have a home away from Cabilis. But you lose your undead effectiveness there, so *shrug*
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