Is this booked in a single reservation (one PNR), or separate tickets? If AA and EY flight are part of the same booking, then EY should rebook you if you miss their flight due to the late incoming AA flight. If on separate tickets, EY will not protect you if AA is late and you mis-connect, and you will need to pay $$ to change your EY ticket.

I personally haven't done a terminal 8 to 4 transfer, so I can't comment on time needed.