Mr.Haren,

The octopus card does help your trip. My suggestions on your route:

take S1 airport shuttle bus (HK$3.5) to Tung Chung, change Tung Chung Line (mtr) to Hong Kong Station. It takes around 29 minutes and costs HK$18.4 WITH your octopus card.

Then walk through the underground passage to go to Central Station, exit J2 and walk to Central Peak Tram Terminus to take peak tram to Victoria Peak.

Another way from HKIA to Victoria Peak: take airport express to HK station, got Central Exchange Square to take No.15 bus to the peak.

You should know that the airport express (around HK90) is more expensive than mtr but much more convenient.

After that, you may get back to Central and take mtr to Sheung Wan. There you can take ferry to Shenzhen. But I've heard that there are few ferries now. Thus, get back to Central, take Tsuen Wan Line to Tsim Sha Tsui, walk to East Tsim Sha Tsui Station to take mtr to Hung Hom. There you can take mtr to Lo Wu. Then cross the border to Shenzhen.