Is expiation obligatory upon one who broke his oath, without definitively saying "Insha'Allah" (if God wills) when making the oath, and without remembering the number of times the oath was made?

If a person swears an oath and says, "Insha'Allah (God willing)," intending it as an exception, then he has made an exception, and he will not be in breach of his oath. Whatever you predominantly believe you have excepted from your oaths, there is no breach of oath upon you and no expiation. As for what you have not, the default is that no exception was made, and expiation is required of you.