2. if you use Windows 8 you will need to rewrite it in WinRT, what do you gain?
Converting a project from .NET to .NET/WinRT is easy if you're not using Pinvokes or unsafe code because most of the classes are still there and work the same.
4. Android phones have a remote wipe facility that sys admins tend to like, not sure if iOS or WinRT/Metro will have this
WinRT is a programming framework and Metro is a process-style, so I'm not sure what them having a "remote wipe facility" would even mean. But Windows8 has a restore to factory settings that is accessible locally (and which an admin could probably script remotely if they really needed to).
6.iPad is proven, tried and tested, WinRT/Metro has a potential to flop as no-one knows of the gamble will pay off yet
iPad is big, but then Microsoft is pretty big too, and they've invested a lot in Metro working on Win8. It's unlikely it will just go and crawl back under a rock.