Brett,
1) Are you referring to XRef's when you ask about files attached to a DWG? If so, Buzzsaw does support XRef's.
2) If you use a business process with the file as an attachment, it will be automatically locked (i.e. it will not be possible to edit it) once the business process is closed (the only way to access the attachment is through the business process itself). If you use a business process and "link" the form to a file in the Buzzsaw file hierarchy, the file will not be locked automatically (but you can manage the form settings to link to a specific version).
3) Buzzsaw does not have any Inventor-specific file structure management.
4) While you cannot create your own business process "from scratch," Buzzsaw Professional provides fourteen (14) standard business processes and seven (7) standard workflow templates. Each template includes routing rules, timers, and email notifications that can be configured for specific processes. You can also create your own forms using Microsoft Infopath, import those forms into Buzzsaw, and connect the forms to the available workflow templates.
Let us know if you need more information.
--Joan Allen