Is sustenance predetermined and decreed, such that it follows a person wherever they go, like death? And does a person's striving for sustenance affect their attainment of it, or does sustenance come to them without striving?

Everything in the universe occurs by the decree and preordainment of Allah, including sustenance. Religious texts have affirmed that no soul shall die until it has received its full sustenance. Therefore, a person must fear Allah and be virtuous in seeking sustenance, taking what is lawful and forsaking what is unlawful. Furthermore, they are required to strive and earn through legitimate means, even if their sustenance has been preordained for them.