3.
You cannot drop a datafile, you only can drop a tablespace and afterwards delete it's datafiles. ( on 9i, when using Oracle Managed Files, the files will be deleted automaticaly, or use 'drop tablespace .... including contents and datafiles' to automaticly remove the datafiles while dropping the tablespace )

4.
When you use the dbca, and choose the datawarehouse db, all the dwh-tools will be installed.
If you choose to define you own database ( using the dbca ) you can decide wheter you want to install the option or not.

5.
Read the datawarehousing guide to get a grip of the oracle dwh features.
For more general info on dwh, you can read the Kimball book. ( here is the url to amazon.com : http://www.amazon.com/exec/obidos/AS...656457-5118336 )

HTH
Gert