Aricept...I started my dad on it last week. Any thoughts?

NOTHING will stop or cure Dementia of any kind. My mom is on Aricept 10mg as well. I honestly can't tell you that it has worked or not. Her memory issues have progressed quite quickly. 
She was started on it Feb 2017 but unfortunatly it may have been to late to have any real effect..

How about reducing hallucinations?

Did NOT stop ......

My wife took 10 mg daily for 3 or 4 years but it stop her from developing full blown AZ. She is in an Alzheimers care facility now. My opinion is Aricept may slow the onset of Alzheimers but at least in my experience it didn't stop it. Of course no one ever TOLD me aricept would STOP the disease. I DID learn that many drug plans charged $250-300 for a 30 day supply of ARICEPT but that some on-line drug plans charge as little as $10 for the same 1 month supply. AT THE SAME PHARMACY.