Hi Paul-W,
This is the way I would recommend to move further that .
1. Create a Company with all the masters and setup in place.
2. Copy and replicate the companies and rename the companies as per BU.
3. Create a Company (Parent) which will contain all the consolidation of all G/L.
In order to synchronize different CRM BUs with BC, you can use WebServices which are unique to each companies.
Let me know if you need further help.