1. They go into the 'Messages' icon, as well as their own individual icon for the BIS account.
3. Sorta. Each BIS account already has its own messaging icon. If you want your users to have a separate icon for their BES messages, then you can enable 'Enterprise-Only' message icon on the BES. KB15003 - Turn on or turn off the Enterprise-Only Message Application in BES - Port3101.org : Your BES Connection
5. Way too many to list. Primary deficiency is lack of wireless PIM sync for BIS.
6. No reason other than OWA might not be available for the user.
7. Yes, the BES data plan includes BIS.