Thank you, Robert.

Souls are a spark of god himself. When they're incarnated on earth, they're expected to know everything that there is to know. Since it's a long process, it gets involved in the cycle of death and rebirth to finally get released (reach Moksha or Nirvana).

There is no particular consent, the soul is a part of god and he decided to do all of this upon his own wish. However, it is in the hands of the soul to get out of it. That is when it is said that the soul becomes one with god.

Yes, you're right, most people's Karma seems to balance out to the negative and that's because the soul is still in the process of learning. The closer he is to reach his goal, the lesser negatives he has (since he becomes entirely aware).