1809 is patched enough to be usable now. It's a little less snappy and IKEv2 for VPN is broken. Some people report audio issues so don't trust the drivers Windows 1809 installs for you, have the drivers of your OEM ready. In an effort to make the kernel more secure, they ended up breaking old and new drivers so you if you run into those issues know you will have to experiment with drivers. What used to work in 1803 may no longer work in 1809. That's my experience.
But as I tell anyone who asks me in real life and on the Internet, backup backup backup. And keep that backup for at least 1 month! Just in case something goes south you can just restore a backup instead of tedious reinstall.
The most dangerous part of 1809 is the upgrade process. There are so so many issues. I had to upgrade 3x. On the third try it worked. Windows seems to break itself during installation so be prepared for that. If you upgrade and 1809 is using a lot of CPU or acting sluggish, something broke because the same things happened to me. I restored my backup of 1803, turned off my AV, redownload the ISO and tried again and it worked 90% but it still acted buggy so I followed this guide to restore health which repairs the Windows image:
How to use DISM command-line utility to repair a Windows 10 image
After that it finally acted normal. Once you have it at a point where it is stable, do another backup before you start tweaking settings. 1809 is definitely more "sensitive". I learned the hard way. Good luck!