Once installed base ArcSDE and Oracle
How I organize my features at the base, with that user and that scheme should save all features.... basically structure and organization at the base.-
Create a schema owner or owners to host the spatial data.
From ArcCatalog connect as SYS and create the new user
you can create more than one schema owners depend the data you have and way you want to organize the data
for example a schema owner for the Vector and one other for the Rasters
or a schema owner for the Operational Data and one other for the Basemap Layers
or a schema owner for the Public Available Data and one other for the confidential........and so on.
Also keep in your mind that the different schema owners can help you to manage better the DBMS backup.
For example the a schema with static spatial data (e.g images) does not need to participate in to the every day backup process.