I don't think it's a bad kit. The detail is good, the fit is ok, the instructions have one ambiguity regarding the main gear. I found that not including the cargo floor greatly simplified the kit. And when finished, it's good looking.
That is an air intake. There was a gas powered APU under the cockpit floor, to charge the batteries and start the engines on the typically remote and generally primitive air fields in China. Later that was moved to a shelf in the cargo area.