Hong Kong CityView Hotel and Luggage

1. Yes, you can.
2. No reservation is needed. Just show your boarding pass and Airport Express train ticket, and you can get onto the bus.
The free shuttle bus line K5 is available from 06:12 to 23:12. The frequency is 20 minutes. The duration is around 10 minutes.
Then, transfer to take AE train to HKIA (about 20 minutes).
Generally speaking, you need to reach HKIA at least two hours before departure.