Constitution can be kept at 16, there's no real reason to go above that beyond regeneration that can come through the Machine of Lum the Mad - why would you do that, god knows.
Wisdom, as far as I know, has nothing to do with Monks in BG. Intelligence is good to have at x*5 so that with a tome of intelligence you get to either 6, 11 or 16 (Mind Flayer protection). Charisma, all the rest really.
@TJ_Hooker The claw is universal, unless there's a restriction unmentioned in its description. That would imply even Wizard Slayers can use it, oddly enough, and is why a Con of 17 or 18 is ideal for every class.
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Proficiencies, since they're high THAC0 thieves, Single Weapon Fighting, Scimitars, and Short Bows (short bows are badass).
Wisdom, as far as I know, has nothing to do with Monks in BG. Intelligence is good to have at x*5 so that with a tome of intelligence you get to either 6, 11 or 16 (Mind Flayer protection). Charisma, all the rest really.