Don't Install macOS Sierra if You Aren't Prepared
Do you have a Time Machine backup of your Mac? Do you know all your passwords? Can you spend an hour without using your Mac right now?
If you can't answer yes to all those questions you shouldn't install macOS Sierra right now. With macOS Sierra 10.12.4 and later this is even more important considering this upgrade. With macOS Sierra 10.12.4 the Mac switched to the Apple File System, which could cause issues. If you are upgrading past 10.12.4, you will make this conversion during this update. This makes a backup an essential part of this upgrade.
The chance that you will lose data is very slim, but it can happen so it is a good idea to have a backup. Read up on how long the macOS Sierra update takes before you get started.