The first error simply means you haven't defined the language plpgsql. The easiest way to do this is to log in as the postgres user, and do a "createlang plpgsql your_database_name". Then you'll be able to define functions.
The other messages aren't ERRORs, they're NOTICEs telling you of extra things Postgres is creating implicitly as a result of the datamodel definitions. Ignore them.