Bajie said, "Master goes in — but is it really all right for us to stand about in front of a government office?"

衙門 is the yamen, a local government office where the official also lived — the word came into English in the nineteenth century and is still the ordinary Chinese for a government building. Bajie's question is not stupid. Three creatures of his description loitering outside a magistracy is exactly the sort of thing that ends in a disturbance, and it very nearly does.

Tripitaka said, "Can you not read the three characters over that door — Guest House?

A rare moment of sharpness from Tripitaka, and the sentence carries a doubled question-and-exclamation mark, which the text preserves. 待客館 is exactly three characters, and the novel counts them for us: the sign says receive-guests-hall. His point is that Bajie is standing next to an answer and asking the question anyway.

Go and sit yourselves down in there, see whether there is fodder, and buy some to feed the horse.

草料 is fodder, grass and grain together, the standard word for what you feed a horse on the road. The instruction is entirely domestic and it is doing something useful: it gives three conspicuous disciples a reason to be indoors and occupied while their master handles the officials.