I am interested in purchasing Spark for a project, I would like to know if there is any inbuilt functionality for failed subscription payments (grace periods or notifications) aside from the obvious of suspend/cancelling the subscription.
You set grace periods and notifications for failed charges in the Stripe Dashboard, not in Spark. There is no real "extra" handling for a failed payment on signup because who wants a customer using a bad card? Although, you can intercept Spark events and handle it on your own.