1.for EAD you have to send your application to service center
2 if you don’t get your new EAD before your EAD expires and you still continue to work with expired EAD then your employer can be fined not you, make alternative arrangements to take the salary, your employer HR can fix this if they really want to help you.
3 if 90 days passed after applying for EAD then you can go to local INS office to get EAD with EAD filing receipt