Again, the amount of properties under your name doesn't matter. The extra tax is if the buyer purchases a second property.
If you are holding the property under home return permit the bank will force you to exchange the money to HKD and transfer to HK. If you hold it under a foreign passport you can transfer USD to your home country. There are no restrictions on the amount you can transfer overseas if you are NOT a Chinese citizen AND have proof of taxes paid.
The person buying the apartment is probably gonna take out a mortgage and the bank won't allow something shady like half cash, half wire transfer. I wouldn't recommend it either way, that's a good way to get scammed. Usually the buyer will pay you 10% deposit into your Chinese bank account, then you and the buyer will open a joint bank account at the branch the buyer will get the mortgage from. The buyer transfers the down payment into that account, you both go to the property bureau to transfer the properties, you will get your fingerprints and a photo taken, depending on your contract the buyer will use his bank card to pay all the taxes on the spot, after a few days the bank will pick up the new property book, you both go to the bank with your ID, you will get your money released to your account and the buyer will get a stamped copy of the property book with the bank keeping the original. Sometimes the bank will force you to open a new account with them to have the money released into.