Well, I just keep it updated, and don’t use a lot of plugins. The only two I use are discourse-affiliate (which unfortunately only does Amazon-links, and not even UK-ones) and retort. I do have the standard ones enabled.
It’s been relatively unproblematic, although I am thinking about storing images externally (S3 or Digital Ocean Object Storage).
As for financing, I run ads on the main site, not the forum. The reason for this is, that people can donate to have the ads removed, and I haven’t worked out how to turn ads off for some users on the forum, so I left it ad-free for now. If I were just running a forum, I’d probably just throw some ads in there (though I’d like to be able to turn them off for some users).