I read through the tutorial and it sounds good, but the website @lojze linked to is old and outdated. Entering user preferences in ~.fonts.conf (/home/YOUR_USER_NAME/.fonts.conf) is deprecated and has been for a couple of years. With some apps this will generate fontconfig error messages in your logs or at the console. The preferred location now is “~.config/fontconfig/conf.d” or " ~.config/fontconfig/fonts.conf" (/home/YOUR_USER_NAME/.config/fontconfig/fonts.conf).
I’ve used the Infinality patches on my old Gentoo install for years. It was a great idea back when there was BCI licensing issues, and disros shipped with the crappy autohinter enabled, but now that the patents have lapsed and and every distro ships with the BCI hinter is enabled by default, it’s a lot of work to have a minimal gain IMHO. The free fonts that used to come with distros as default were designed for the autohinter and didn’t render well as they scaled to different sizes.
A better method for great fonts is to scan through /etc/fonts/conf.avail and /etc/fonts/conf.d and enable or disable the symlinks there between them to your liking. Then create a fonts.conf file in the location I previously mentioned that properly aliases and substitutes your preferred modern fonts for for those old default free ones. For example, I use Droid fonts for my KDE Plasma5 workspace, then I set-up Noto fonts to be used instead in my fonts.conf file so that they are used in my browsers.
In KDE it’s extremely easy to see what different adjustments do because the font control panel applet allows you to enable or disable a number of font features. Then when you have your preferred fonts rendering correctly you can add those settings to /etc/fonts/conf.d symlinks or /etc/fonts/local.conf to affect all users in a multi user setup, or in your ~.config/fontconfig/fonts.conf file for your user.
Call me old school, but like I said, I used to use the Infinality hack. But now I prefer using more modern better fonts that are properly configured with the default FC. Doing things this way you are much less likely to have unwanted side effects, like unexpected crashes due to font config errors.