What should I do regarding the multiple vows I made and forgot to fulfill? Is one expiation (kaffara) for an oath sufficient for all instances, or is an expiation required for each instance? What about the vows I don't remember at all or only partially? And is not fulfilling them a cause of calamities and unanswered prayers?

"Excessive vows are not recommended, especially if they are conditional. They do not change anything. However, if the condition upon which the vows were made comes to pass, then all of them must be fulfilled, provided they are acts of obedience to Allah. One expiation is not sufficient for all of them. If you do not fulfill them while being able to, then you have disobeyed Allah."