May I clarify that taking mtr to tung chung means already reach lantau island? Taking the cable car just allow you to have the panaromic view and a ride to the buddha?

You are totally right.

To visit Tai O, take Tung Chung Line to Tung Chung MTR Station. Then take No.11 bus to Tai O Bus Station.

Can I go Tai O first before I visit the Buddha and then later get to citygate shopping complex?

Please arrange your time appropriately if you intend to use Ngong Ping 360 Cable Car from Tung Chung Cable Car Terminal.

Opening hours of Ngong Ping 360 Cable Car:
Weekdays 10:00am - 6:00pm
Weekends & Public Holidays 9:00am - 6:30pm