How can one reconcile the fact that intention (niyyah) is the resolve to do something and does not require its recollection before the act, with the multiplicity of intentions before worship for those with excuses or in charitable acts?

Intention (Niyyah) is an aim or purpose, and its place is the heart. It is a condition for the validity of worship. As for uttering it verbally with the tongue, that is not prescribed. It is permissible to combine several intentions as long as they do not contradict sincerity to Allah Almighty. The time for the intention is a short while before the act or the commencement of worship. Bringing something to mind inwardly is not considered verbal utterance, because verbal utterance is specific to what is pronounced by the tongue.