Many HostStack customers keep DNS at Cloudflare (or another DNS provider) while hosting files and databases on HostStack. That setup works well when you align three things: A/AAAA targets, MX for mail, and proxy mode expectations.
If Cloudflare proxies HTTP (“orange cloud”), your origin sees Cloudflare IPs — fine for most sites, but you should confirm SSL mode (Full vs Full Strict) matches certificates installed at HostStack.
For mail, avoid proxying MX hosts; keep mail-related records DNS-only unless your mail provider documents otherwise.