I hope you don't get any more problems.
About the lost files, it's always best to keep backups of important files on a USB external drive or other storage. Losses can occur not only when upgrading the OS but also for other reasons such as hard disk failure or total failure of the OS. Keeping backups on an external drive (disconnected when not in use) also protects them from malware.
Regarding the upgrade, operating systems mature as time goes by. The developers learn about shortfalls one way or another and they issue updates to fix them. This happened with Windows XP and Windows 7. Service Packs containing improvements were issued some time after the operating system's initial release dates. Same with Windows 8.0. Another point is that Microsoft are stopping support for Windows 8.0 in October next year. This is probably the reason why Windows 8.0 users are now not able to opt out of the upgrade to Windows 8.1.
When reading around the Internet, It might seem that upgrade problems are more likely to happen than not. However, I think cases of people experiencing difficulties would probably be far outnumbered by the millions of people who don't
get any trouble. Those who don't get problems are not likely to want to write about a trouble-free upgrade experience in forums, blogs and Internet articles. We mostly only get to hear about cases where things go wrong.