#1 If you are on the company BES, you shouldn't have to delete messages twice. If you have the BIS account set up to pull email from your office email address, there's no way to "synchronize" delete through BIS.
#1b If you are using the company BES, you can use redirector settings to disable forwarding when in cradle. This tells the BES to not forward email when your BB is connected to the cable. (sorry, forgot this and had to edit my post to add it).
#2 The desktop redirector software only works if you have a Microsoft Exchange Server. It does not work with just Outlook. You need the server in the backend.
#3 To clarify what Julian said above, the key you are looking for is the shift key. to the right of the space bar. Hold that while scrolling.
#4 You've already found a solution