You need to set the Oracle_sid for which you are starting and shutting down
Set the SID then do your sqlplus, then connect sys/password
For our shutdowns we use shutdown immediate rather than transactional. If someone is logged in to the database with a transaction started and not commited the database will set and wait for the transaction to commit before it shutsdown. If theis person is gone for the night the db will never shut down
Don't be afraid to try something new. Amateurs built the Ark, professionals built the Titanic