Aside from that, nothing is required. You could beat the game with all skills at 0 if you wanted, although killing things would be annoyingly slow. Evading monster attacks is the important part.
The game has unlimited experience available to level up and get more skill points, so you cannot actually lock yourself out of beating the game.
As far as skill balance goes:
SpoilerShow
Light weapons are by far the best weapons, much like the situation with swords in Grimrock 1, and an optimized party almost certainly has two light weapon users.
Throwing weapons are also far better than missile weapons or firearms.
Unlike in Grimrock 1 you actually get enough skill points to train more than one skill, so even the light weapons users will have skilling decisions to make after you max Light Weapons and Critical.
Again, though, the important part is evading monster attacks. Unlike in Grimrock 1, you cannot stunlock monsters, so standing in front of one and swinging is going to be bad no matter how optimized your party is.
Throwing weapons are also far better than missile weapons or firearms.
Unlike in Grimrock 1 you actually get enough skill points to train more than one skill, so even the light weapons users will have skilling decisions to make after you max Light Weapons and Critical.
Again, though, the important part is evading monster attacks. Unlike in Grimrock 1, you cannot stunlock monsters, so standing in front of one and swinging is going to be bad no matter how optimized your party is.