How is your Ecobee connected? Via Smartapp or Linked service?
If it’s Link d service then you don’t. Need to do anything
If it’s through a Smartapp like Ecobee Suite then that will stop working and you will need to switch over to the Linked Service. You will loose functionality when you do this since the linked service does not have all the bells and whistles that the smartapp do. You can read more about alternatives here
This has been requested but none has built an alternative for the FKB DTH. I believe you can do something with it using the webrequestor driver by Tustin but you have to host part of it on your own server.
This means they have not been converted to Edge drivers yet. Look in the IDE for the fingerprint and then you can search the forum for a driver or look in the SmartThings GitHub and see if the fingerprint is in a driver.
Yes. Webcore is groovy based and will no longer work. Several people are starting to use SharpTools rule engine but it is not as robust and you have to rethink a lot of your logic when recreating pistons. You can find several discussions on SharpTools in the forum. Although since you already use Action Tiles that may not interest you.