I am going to provide you some info based on what I know from my experiences.
For example are you guys ready to throw out Cisco 2960X to be able to use VXLAN and SDA?
-I can tell you right now (today) that 2960s are not supported as being compatible/supported with SDA. Take a peek at the matrix to see compatibility: Cisco Software-Defined Access Compatibility Matrix
What do you guys think about new 9200 model switches?
-Can't really relate to this one as in our environment we run mostly 93/9500s.
(Advatage and Essential) As far as i know Essential models are like L2 switches even if you take 9300 ?
-Take a peek at the following link as it will cover all of the features and differences: Enterprise Networks Software Subscription Matrix for Switching - Cisco
old 3850 which is L3 or i don't understand their new system
-3850s can participate in an SDA deployment in the following roles: Fabric Edge, Fabric Border & Control Plane Node. My recommendation for longevity concerns would be to go with 9k devices. 3850 EOL announcements: End-of-Sale and End-of-Life Announcement for the Cisco Catalyst 3850 switches - Cisco
Good luck & HTH!
