1. Does the modal may have a future form?Ex: Such defects may easily lead to serious breakdown.Modal may doesn't have a future "form".
2. Does to be to have a future form?Ex: I am to call them once I reach the airportIn the example, 'am to call' is short for 'am supposed to call', which doesn't have a future form; e.g. *I will supposed to call.
3. Does should have a past and future form?Ex: You shouldn't drink and drive.
See ENGLISH PAGE - Modal Verb Tutorial