It has been awhile since I've played this game. You may want to check out the math appendix of the
Beyond Divinity Strategy Guide.
There is a typo in the last formula in the 'other secondary stats' section; in the formula for evasion, the second term should be speed, rather than survival.
You do need to judge your needs by practical results. There are many ways to build a viable character, and what you need also depends on your playstyle. The math appendix makes some general suggestions on stat point distribution, but even just with warriors some people have made high strength/damage builds with low accuracy, or high agility/damage(Sharpen) and accuracy, or moderate damage high accuracy, etc.
I only put a point or two into the accuracy sub-skill in weapon expertise. The first point gives a good bonus IIRC, but after that you don't get as much for additional skill points. I didn't put much in the damage sub-skill either; the only one I made sure to max was the Reload Time for bow and crossbow expertise.