Is it permissible to fast as expiation for an oath (kaffarat al-yamin) instead of feeding or clothing, due to financial inability, knowing that money will become available later?

The order of fasting, feeding, clothing, and freeing a slave in expiation for an oath is obligatory, as Allah the Almighty says: ﴿Its expiation is the feeding of ten poor people from the average of that which you feed your [own] families, or clothing them, or freeing a slave. But whoever finds not [the means to do so] - then a fast of three days. That is the expiation for oaths when you have sworn. And guard your oaths.﴾ (Surat Al-Ma'idah, 89). Thus, fasting is not sufficient if the swearer has the means to feed others beyond his own sustenance and that of those whose maintenance is incumbent upon him, according to the majority of scholars.

It is not permissible to delay the expiation according to most scholars, because the command implies immediate obligation according to them.

If the repeated oaths are concerning one single matter, then there is only one expiation. But if they are concerning multiple matters, then each one requires an expiation.