I am too individual running my own mail server and gmail don't reject my mails. I don't even have SPF or DKIM on my domains. I think most common mistake is making mail server out of cheap VPS. Don't do that. Your IP reputation depends your digital neighborhood. Blocks happen even /16 level, entire VPS provider networks are on special lists in some mailservice providers. Additionally, those IP-s are reused, so there is nice chance to get some hit-and-run spammer IP and that is lots of work do clean that up.