It looks like Exchange knows all about the "SBS Web Applications" Virtual Directory, so as long as there is no port conflict with "Default Web Site", you should be OK. If "Default Web Site" is listening on port 80, to service OWA, EWS etc, what port is "SBS Web Applications" using ? They can’t both be using port 80, unless you have multiple IP addresses.
Your InternalUrl and ExternalUrl both have HTTPS listed as the protocol, but WebSiteSSLEnabled = False. You don't want to use SSL so drop the "S". Is the "SBS Web Applications" web site running ?
