Hi,
You don't need any SAN storage for your Consolidated EDGE server as there will be no content hosted on that server. All data resides on your Front-End Servers in your internal network.
The only reason you would need SAN Storage is if you where doing boot from SAN deploments which in that case you will only need to size your OS volume which is whatever standard you have today for such a server. Something higher then 20GB would be sufficient.
Sincerely,
Tonino Bruno