Is it forbidden to swear an oath for every action one intends to perform, especially if the purpose of the oath is self-compulsion to avoid abandoning the work or committing a sin? And is there a sin incurred for not completing the sworn-upon work entirely due to lack of time?

Frequent swearing is dislikable (makruh tanzihi), not forbidden (haram). Fulfilling an oath is not obligatory unless it concerns the performance of an act that is a religious obligation or the abandonment of something forbidden.

Whoever swears to do something disliked or to refrain from something recommended, it is sunnah (recommended) for him to break his oath, and it is disliked for him to fulfill it. And whoever swears to do something recommended or to refrain from something disliked, it is disliked for him to break his oath, and it is sunnah for him to fulfill it.

Whoever swears to do something obligatory or to refrain from something forbidden, it is forbidden for him to break his oath, and it is obligatory for him to fulfill it.

And whoever swears to do something forbidden or to refrain from something obligatory, it is obligatory for him to break his oath, and it is forbidden for him to fulfill it.

As for whoever swears to do something permissible, he has the choice between breaking the oath and fulfilling it, and preserving the oath in this case is preferable.