Dumb question: in Cryptonomicon, there's a character named "Goto Dengo". Is Goto used as both a first and last name, or is the notion of first and last name something that doesn't map cleanly between English and Japanese?

In Japanese, you write family name first. Sometimes when using a Japanese name in English, you flip them to the English order, and sometimes not.

Japanese family names go first. e.g., GRAHAM Paul.

Respectfully, that's not such a good example, as both of those names can be first or last names. DOE John would be a better example.

The example is referring to a certain famous Graham Paul, for which people here are assumed to know what's his actual first and last name.