I would take the van from HKIA to Huanggang for HK$150. If you don't have HK$ and rmb then draw from a dual-currency ATM in the arrival area. Follow the signs to Mainland Trsnsport for the short walk to the waiting area and buy your ticket and they'll put you in the next van 5-15 minutes wait.
You will exit HK in the van and it will drop you at China immigration. If you only have rmb100 notes buy a bottle of water or a cold beer to avoid the "I've got no change" taxi driver game. Cross the footbridge to the legal taxi rank (there is an escalator if you look hard enough), join one of the queues, and show the driver your hotel name written in Chinese. Cost of that trip is about rmb20-30. Total time from HKIA to your hotel should be just over an hour depending on the queues at China immigration.
You can get to Yitian station by taking a bus and three metro rides for half the price, twice the time and three times the hassle. Yitian is a long way from Shekou or Shenzhen Bay.