Don’t turn them off domain-wide, do this with a rule:
Minification, Rocket Loader, Mirage and Polish should all be disabled. ‘Disable Performance’ achieves this.
Brotli compression is also unnecessary and has previously caused issues, it can be disabled at domain-level in the ‘speed’ section of the dashboard.
The only area where Cloudflare can really assist Discourse is with asste caching, feel free to create a secondary rule which enables cache level ‘Standard’ on /uploads/* if you don’t employ some other form of CDN.