What is the optimal course of action with a young man who wishes to marry but does not propose due to the unavailability of a good job, coupled with fears of constant rejection for those who propose, and regret in the event of approval?

The recommended approach is to choose the best suitor in terms of religiosity and character, and to accept him after performing Istikhara (prayer for guidance). There is no impediment to waiting for a specific person and rejecting other suitors, while being aware that repeatedly rejecting suitors without a valid reason can lead to undesirable consequences.