Is a person held accountable for unintentionally touching or looking at a woman? Is he rewarded for every deed he performs in his life? And how does one overcome the obsessive whispers regarding istinja'?

There is no sin upon you for an accidental glance at a non-mahram woman as long as you avert your gaze from her immediately. You will also not be held accountable for unintentionally touching a woman's hand. To rid yourself of whispers (waswās), completely disregard them and do not succumb to them.