0. Use the docker version
1. use maxsize memory flag to keep the memory under control
2. set up a cron job to kill/restart it in the middle of the night, every night.
3. use a reverse proxy to hide the address at least a little bit
Their product is both ridiculously overpriced for what you get ($30/month, last I looked, for a spelling/grammar checker along the lines of what MS Word provides), a massive privacy/security violation (you have to send everything you type for the service to do its job; no corporate IT with a pulse would be okay with this), and worst of all, it's buggy as hell. Last time I tried it, it refused to work on HN even though this is a bog standard text field, and I spent a ton of time trying to get it to stop correcting things that didn't need corrected.
Check Settings → Natural Languages → Grammar → Rules for all available grammar rules.
That said, I am not a power user and my English is just passable, so your mileage may vary.
[1] https://languagetool.org