How many DC's & XenApp servers to support 600 users

Looking for recommendations.  I need to put in a request to get our production environment ready to go for XenApp 7.15 though we are still working through base configuration in non-production.  

Since the Delivery Controller's in XenApp 7.15 do not also act as a XenApp box to deploy applications as they do in 6.5, I wanted to throw out here what I'm thinking to support roughly 600-650 concurrent users.

Current Design (XenApp 6.5 Farm):

1 - License Server
Non-Production:
•      4 – XenApp 6.5 - Main STA’s
Production:
•      5 – XenApp 6.5 (1st  Subnet) - Main STA’s
•      13 – XenApp 6.5 (2nd Subnet)


Proposed for XenApp 7.15

1 - License Server
Non-Production:
•      2 – Delivery Controller’s (Scout, Studio, Delivery - STA)
•      2 – XenApp 7.15

Production:
•      4 – Delivery Controller’s (Scout, Studio, Delivery – STA)
•      3 or 4 – XenApp 7.15 (1st  Subnet)
•      13 – XenApp 7.15 (2nd Subnet)



Any thoughts are appreciated.

Thanks