brew install npm "npm: command not found"
I encountered the same issue. After searching and reading different things online, what worked for me was:
$ brew postinstall node
However, first please do execute:
$ brew doctor
and follow the instructions there first, like the comment in your question mentions.
Try the following:
$ brew update
$ brew uninstall node
$ brew install node
$ sudo chown -R YouComputerName /usr/local/lib/node_modules/
$ brew postinstall node