5.8 was a typo. It should have read 5.9. I was updating the 5.8 repos when I wrote that
The 18.104.22.168 kernel does not fix any security issues so that kernel isn't mandatory. What it does is add support for newer hardware and fix some bugs. There is also a 22.214.171.124 kernel that you could use.
The failure message on the modules means that *one* or more kernel modules didn't load. It doesn't mean that all modules failed. Did you have the novmsplice patch installed on your original 126.96.36.199 kernel? If so that is what's causing the error. It isn't needed and doesn't work with the newer kernel. Comment out the line referring to it in /etc/rc.d/modules (done as root in your favorite text editor) and that error will go away.
If it isn't novmsplice then you can find out what is causing the error by examining your logs. Find your last boot sequence in /var/log/messages and you'll be able to see which module isn't loading and if it's actually important or not. It could be your configuration is trying to load a module for hardware you simply don't have.
The font caching failure is an entirely different issue not related to the kernel. Do you have access to all your installed fonts in your favorite word processor? Have you installed the fontfix patch? Check in gslapt to see if you have a package called fontfix installed. If not, well... it's in patches for a reason. Make sure the patches repository is enabled in gslapt. You can check that by clicking on Edit->Preferences and choosing the Sources tab. You should always have packages, extra, and patches checked off. As a general rule you should not have testing checked unless you want to test a specific new package.
Doing updates: There are two methods. One if to upgrade specific programs where you want a security patch, a bugfix, or a new feature. You just do an install with either slapt-get or gslapt and the upgrading part (removing the old, installing the new) is handled pretty much automatically. The only exception to this are kernel packages. They should NEVER be upgraded. You did it the right way already--install the new alongside the old. That way if you have a problem with the new you can boot into the old and go back to what you know works on your system.
The second option is a system-wide upgrade. This is what distros like Ubuntu and Fedora recommend. A system-wide upgrade replaces all packages with the latest and greatest version for the release of VL you are running. It will not replace 5.9 packages with 6.0 packages. The advantage of a system-wide upgrade are that you know your system will have every possible security vulnerability patched and any known significant bugs will be fixed. The disadvantage is that you may get upgrades you don't really need for your system and the more you change the greater risk of breakage. I have done system upgrades with VL religiously and I have yet to break anything in 5.9 but, as always, YMMV. I'll also add that I'm running Light rather than Standard at the moment.
OK, if you decide to do a system upgrade that is only available at the command line. You MUST
have patches enabled before you try this. As root you type:
It takes a while but everything from Firefox to AbiWord to WiFi-Radar as well as more core things like X and CUPS (printing) will all go to newer versions.
There is no "correct" method. The method you choose depends on your needs and how you want to manage the system. In Linux, and in UNIX as well, there are always several different ways to get things done.
I hope I haven't made things as clear as mud