It took 130 days to make it halfway, and they crashed off the Aleutian Islands.
The first sort-of-successful flight around the world was by the U.S. Army Air Corps.[1] Five planes started, two finished. Along the way, five engine changes and two wing changes.
The Graf Zeppelin, in 1929, made the first real circumnavigation of the earth, carrying passengers and without a major rebuild enroute.
[1] https://en.wikipedia.org/wiki/First_aerial_circumnavigation
I've always thought seaplanes were very cool, yet they've almost completely gone away from commercial air transportation.
What's the reason for this? Are they just too hard to maintain because of salt water etc.?
Well there are a number of reasons, the primary reason being is that there is no need for them as any place that supports commercial air transportation has an airport nowadays. So why make a separate model that can't fly inland? Secondly, if its a seaplane vs flying boat, the floats are not good for aerodynamics. I would suspect on flying boats the design compromises to make it work on the water would bring other issues that would make it difficult to compete with land-based aircraft. There are definitely smaller operations, for example in the Pacific Northwest that use seaplanes/amphibians for island hopping, and they are used in bush operations in Alaska and northern Canada. I flew on a seaplane out of Lake Union to do an aerial tour of Seattle.