Been self-hosting Nextcloud and using two managed Nextcloud server. All of them were terribly slow. Had a few strange bugs and the self-hosted one just stopped working without any known cause. The Android app is also buggy, freezes often and I had to resort to a third-party app because of these problems. And don't even let me start talking about extending Nextcloud with NC apps. Tbh Nextcloud feels like Beta software all over the place. I would never use it for something which needs reliability, like a business.
I also would advice against self-hosting for most users. There is so much to take care of and one small misconfiguration could put your server and data at risk. If you are not versed at self-hosting, it will be a massive waste of time. If you nevertheless want to self-host, put it behind a VPN or Cloudflare Tunnel to have an additional layer of security.
I haven't found the perfect solution so far. Cryptomator + Office 365 Family with up to 6x1TB Onedrive is the unbeaten price champion if you need up to 6TB or need to buy MS Office anyway. I am unsure how much Microsoft can do with metadata and telemetry in this case. And the question is how do you deal with contacts and calendar in this case, which can't be easily encrypted synced? Etesync is in theory a good solution for E2EE contact and calendar sync, but their Windows solution looks more like a hack than a proper solution.