I spent four years in China with an airline so my GA knowledge of China is limited as is I believe that of most Chinese controllers. Metric altitudes will probably be the least of your worries. Flight plans must be filed well in advance and subject to military approval. Controllers aren't used to handling GA flights depending on where you want to go. Most airports probably won't have Avgas or limited availability at best. Use caution with ATC communications since I assume none of your group and that I the ATC controllers have English as their primary or native language.
The devil is in the details. Get those all worked out and enjoy your trip. China is a beautiful country.
Good luck.