If the money is not an issue I would let the agency handle everything for you. Even if you spoke perfect mandarin it would probably be difficult to arrange something like this as it would involve a few trips to government offices where nobody there would be too interested in helping you out although in Beijing you'd probably find someone at each office who spoke passable English. It would not be a good way to get adjusted to a new country!

If you have a good agency do it for you they will have contacts at whatever government ministry you have to go thru to import your cat and things will be hastle free. If you do it yourself you are inviting a hastle!

I get stopped about every other time I go thru a Chinese border crossing because I have a piece of fruit in my bag. I'm think they would stop you if you just tried to carry your cat in.