Roundtrip Madrid-Shanghai-HongKong-Shanghai

Hello,

thnaks for your comprehensive guide and work you put into it! :-)

I want to start a business and import goods from Shanghai. Instead of sending samples and waiting more than a month, I thought maybe I just fly over to convince myself.
Now, if I book a flight from Madrid to Shanghai, stay 3 days, fly to Hongkong, stay there for 2 days, fly back to Shanghai, stay there for another day and fly back to Madrid - is this a scenario that is possible? I colud also fly back from HongKong but the flights are much(!) cheaper with this flight schedule...

Do I have to apply twice for the Visa?
Thanks so much,
Thomas