I think that is unchanged in v5, there is a sort of workaround procedure (should be FAQ?)
1. Open destination project
2. Use "Append sheet" to copy sheet from source project
3. Copy/paste within project
4. If no longer needed, delete appended sheet
i think this will be easier in V5, since you can add a symbol library to the global table so it will appear in all projects.
Not really, it is a new feature which I have not tried yet. I believe it is a similar scheme to the footprint library table management.