1. You could take MTR from MTR Tsuen Wan Station - B2 to MTR Causeway Bay Station - D1. Then transfer bus 5 from Near President Theatre, Cannon Street to Shouson Hill Road, Opposite house no. 3A. You will see the Ocean Park.
2. You can either exchange your money into HKD in Ph or HK. Maybe better in your country.
3. I think 3 days is enough to visit HK. The first day, you can go to visit the Ocean Paek, the peak , Repulse Bay and the Central. The second day, you could go to the Disneyland an Ngong Ping 360, plus the citygate outlet. The third day, you can go to Tsim Sha Tsui and Mongkok for shopping. Anyway, you can refer to Hong Kong Tours(https://www.travelchinaguide.com/package/hongkong/) to make your travel plan.