Plenty of solo amateur web developers, some of them teenagers, were doing this stuff alone 12+ years ago. I was one of them. I'm not saying my code was elegant or secure, but it tried to solve the problems you have described (maybe not working in multiple tabs, that wasn't popular at the time). You could develop sites with sessions and databases in PHP using Notepad, an FTP client, and a web host with a database management admin panel. I didn't find out about version control until years later.