If you’re able to install Discourse by yourself, you can maintain it without any issue. I have a ~5000 users forum, with something like 80 topics and 450 messages per month (so, kinda slow for the amount of users I know) and in management I think I don’t spend more than an hour a week. I just enter once to twice a week to update in example.com/admin/upgrade. And that’s pretty much it.
You could also download the backups once a week, and that’s through the dashboard. Then, you sould something like three times a year ssh to the server and update it, update Discourse making git pull; ./launcher rebuild app to ensure everything is up to date.