I have a Deco Wi-Fi mesh of 3 M9 Plus devices.  I'm due to move to full-fibre broadband, which will be supplied with an Amazon Eero router.  Security on the Eero is a subscription service, whereas Deco it's built-in. 

My questions are:

1. Can I get a Deco router (ideally with 4 gigabit ports on the back) that is compatible with the existing mesh network?
2. Could this router then be the Main node of the mesh, leaving the 3 existing M9s working wirelessly?

Thanks in advance.