0. What we can generally see is only up to J9 (9 or more available seats). We cannot tell if there are 30+ seats available. If you see 30+ unassigned seats on seat map, there may just be a few unassigned seats.
1. You can waitlist up to the ticketing deadline. CX will not deduct miles and charge fees at waitlist. So there is no need to refund.
2. Waitlist priority is in accordance with MPC status.