What is the obligatory amount to be disbursed to fulfill a vow, and is it obligatory to fulfill it before settling debts, given that the exact wording of the vow is not remembered?

Your intention determines what is required of you regarding the vow. If you intended to give half of your salary from any job you find, then you must give half of the first salary you received, even if you did not receive it in full. If your intention was for formal employment and full-time work, then you must give half of that salary. If you did not have a specific intention, then you must give half of the first salary you found.

Giving half of the largest salary you have received is better and more cautious.

Debt takes precedence over a vow if the debt was incurred earlier, and the vow takes precedence if it was made earlier, unless the vower specified something particular for the vow, in which case the vow takes precedence.