which bus / buses to get from beijing terminal 3 to Traders Hotel Jianguomenwai Ave Chaoyang?

I don't think bus is the best way to go and there is no direct one. Would you mind taking subway instead? If not, I suggest you take the Airport Express Train to Sanyuanqiao, where transfer to subway line 10 and get off at Guomao. Get out of exit E1 and walk around 400yd to the hotel.

Thank you Fenny. I shall do that.