If you are just self hosting for your own use, just stick with letsencrypt or self signed certificates.
The paid certificates are for businesses where the users need to trust the certificate. They usually come with warranties and identity verification, which is important if you are accepting payments through your website, but it’s just a waste of money for personal use.
You can get rid of the certificate errors by adding your CA to Firefox. Just make sure you keep the private key secure.
Set
browser.fixup.fallback-to-https
tofalse
to stop Firefox from trying https if http doesn’t work.