As far as I've seen there are major changes in the Webforms stuff between Beta3 and RC1. Yes, an updated version of the SDK will be posted to the MSDN Developer Center, but I don't have a date yet. Yes, you can expect some additional changes on the forms. Try using Net Folders instead. It ends up with some temp files and the .doc.
Office first saves a temp file then renames it.
No they don't support RC1. OWA allows this. Exchange 2000 allows this. Just specify a URL to an Exchange resource. When contrasted with Exch5.5 event scripts, it appears that Ex2K is completely re-architected, both in the scripting GUIs and conceptually.