- donate at least 20 things to the Museum, and at least one in each category (bugs, fish, fossils, paintings) and Blathers will ask you to build the second floor of the museum. Some guides say you also have to talk to Blathers every day for 14 days, but I don't know if that's accurate.
- after you've built the 2nd floor of the museum AND donated at least 50 things to the museum (again, at least one in each category), Blathers will ask you to build the Cafe.
And just like Zigzag said, the coffee beans are only good for selling for Bells.
[AC:NL] No random FCRs, please.
Collecting Japanese items