@yuval,

1. There's no Qen although there is Qin (秦), which is one of the top 100 family names and perfectly fine as a surname. Probably wise to avoid anything that sounds like Cohen because of the similarity to 可恨 ("hateful").

2. Just from personal experience, speaking Chinese is what opens doors - a name doesn't do much. So having a good name isn't an impediment, but it doesn't help unless it is particularly good, in which case people are a bit more likely to remember it.