Not OP, but also run my own email server, using postfix, since 2012. It is sad that there is such a widespread belief it is impossible to do unless you're google. Decentralization of basic internet services helps everyone, so if you're at all interested and willing to learn, go for it!
There are plenty guides on setting up postfix. Follow them, cross reference a few, read the docs and use the various free email test sites to sanity check everything. If you've never done it before, expect to dedicate 2-3 days to this.
But don't forget to periodically check the TLS certificate of your SMTP server. Administrators often forget to renew the certificates, and automated renewal processes may also break.
I've seen countless examples of SMTP servers with expired certs. The problem is that you won't notice it, as SMTP will fall back to plain-text communication if the certificate is invalid. So the server will still work with an expired cert.
But if you want to do it right, or if you want to adopt MTA-STS, you usually need to do a bit of regular maintenance on the TLS part.
We've also had some of our users report that an expired cert was hurting their domain reputation for spam algorithms. We have not been able to verify that, but it sounds plausible.
Nearly every time someone suggests against this it's not about issues in setting up the server or receiving emails. It's that many popular providers don't trust random IP addresses sending emails, especially those that 'look like' common spam (such as order invoices from common e-commerce sites like Woocommerce or Shopify).
From an inbox perspective these often look like cold outreach (you've never emailed this company before and the first email they send to you is after you order something) so it's suspicious, and being from a trusted platform helps pass the test.
There are plenty guides on setting up postfix. Follow them, cross reference a few, read the docs and use the various free email test sites to sanity check everything. If you've never done it before, expect to dedicate 2-3 days to this.
Ongoing maintenance is approximately nothing.