Why is Pip surprised by Wemmick’s home? What did he expect?

I think he expected a much fancier home for a man of Wemmick's status.

Pip expected Wemmick's home to reflect the personality he sees of Wemmick at Jaggers' office. He is very surprised to find that it is a "little slice of heaven" having no association whatever with Jaggers office or business. It is a unique, fun, and calm place.