Personally speaking, I think it is best to learn new languages at the same time. This way, you can remember and learn them complementarily, and you can say you have established a basis with Chinese and Spanish. So I guess you have a gift in learning languages. What’s more is that since you want to learn another language and you think Russian fascinates you, you should just learn it, because interest is the best teacher of learning a language. Of course, if you want to learn Chinese better, that is ok, for it is very helpful for your career if you do some jobs related to Chinese or China. Maybe you can have a look at learning-Chinese.
