1) The hold would imply that the OD4B site would NOT be deleted until the hold was released.
2) If the eDiscovery Hold was applied through the eDiscovery center then the document can still be updated, but if it is then a snapshot of the held document will be added to the eDiscovery center so it can be retrieved at that point in time without the changes.
3) If files have been shared then other users should still have access to the file until they are deleted( which won't happen until the hold is removed)