what bus and how much fare from the peak going down to the star ferry terminal or MTR terminal?

From the peak to the Star Ferry Terminal, you can take the bus no. 15C at the Central(Near Star Ferry Pier 8) Bus Terminus. The price is HK$4.20.
If you want to MTR Central Station, you can walk to the station. You can walk along the Garden Road and cross Queen's Road, through Chater Garden, and turn left. Then you can see the station.