1. Sales of your house is capital gain, is subjected to long term capital gain tax. It is not investment income so it is not subjected to NIIT (Net Investment Income Tax).
2. How much is subjected to capital gain tax: the realized gain is (sales price - purchase price - (expenses in purchase and sales)). The whole gain has to be taxed.
3. The capital gain has to paid on the year when the property is sold. The only exception is installment sale.
Installment sales happens when seller serve as the lender for the buyer, and seller get paid in installments, usually monthly. In that case, the capital gain is spread out by the schedule of the installment.
4. China have strict control of RMB to foreign currency, except in two circumstances: emmigration or inheritance of foreign citizens. See this link.