Glad to hear you're thinking of using NodeBB!
As of right now, we don't have anti-spam plugins, though it is definitely a major concern for the platform. Eventually, an anti-spam plugin or CAPTCHA will be added, and installing it on a NodeBB will be as simple as running something like
npm install nodebb-plugin-recaptcha
Ultimately, I'd like to create a plugin that automatically sends post content through a free API that does text analysis and determines link safety, although I have not found a free API for that yet (something like Askimet)