You can take the airport express train to Kowlonn station and then take the airport free shuttle bus service to the hotel. Or you can take the airoport shuttle bus A21 directly from the airport to the hotel.
The cost for the Octppus card depends on your day tour plan.
For the day tours from Hong Kong to Shenzhen, you can try to contact with the reliable china travel agency, Travel China Guide, through this website to ask about detailed information about it.