1) Well, the game is heavily biased towards the warrior, which seems to be the general opinion. The mage can be good as well, but she needs much more babysitting, as she starts pretty frail.
2) Yes, that's exactly what I mean. It is all about luck. You may find 5 full sets and you may find none.
3) You should max the skills you feel that are relevant to your type of play. For example, if you won't use dragons, there is no need to max voice of the dragon. If you won't use orcs, demons or lizards, there is no need to max persuasion.
Use your common sense and you will be fine.
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