To get the extents of all your SHAPE data you can use the BoundingBoxAccumulator transformer.
As for the spatial extents, unfortunately, these can only be set from a Parameter on the Orace Spatial Writer Feature Type (which must be set before the workspace runs) and cannot be set from an attribute value derived during the workspace run.
I think the best approach might be to alter the user_sdo_geom_metadata after you have written the data. That should be possible - see the Oracle Spatial docs. To do this use the FeatureWriter to write you Oracle data, and then connect a SQLExecutor to send the SQL to alter the user_sdo_geom_metadata table.
The alternative is to have a two part workflow, read the shape data to get the extents using BoundingBoxAccumulator and then use WorkspaceRunner to call the workspace that loads your data (and sets the extents parameters).