1) Yes, buy present
2) If you don't have an enterprise bb data plan, yes.
3) No, you can still use the BIS (unless of course your IT Guy says no with BES IT Policy)
4) BES should NOT be installed on the Exchange server, but should be on the same LAN. Worst case, if it can't be, make sure ping times are consistently below 75ms.
5) this really should have been posted elsewhere.