That guide is horrible… let me draft a quick guide here.
If people are interested I will turn it into a how-to original post.
Installing Plex Media Server na CentOS 7
Sources:
Overview
Plex offers several services and the following is recommended:
- Make sure you have decent performance and space on /var. Database and cache takes a lot of space (20GB can be reached quickly) and Plex perfomance depends a lot on performance of this DB and cache.
- Do not worry about amount of directories for the same share
- Do worry about moving from one directory to another (Set up an unionfs for that purpose)
- Do not run Plex transcoding on platforms with poor CPU performance, not worth it for streaming.
- Do not forget to reserve space for Transcodes, this place should handle 50Mb/s read and write (i.e. not a shitty SSD or the same drive as the shares)
Setting up disabled repo PlexRepo
Yum and later DNF is perfect to handle 3rd party binaries and plex does offer RPM builds. You can set it up securely by using yum protect and yum priorities, but we are going to do it the easy way. This only requires the repo to be disabled by default and installing packages from it require manual intervention.
Configuring yum
echo "# Plex.repo file will allow dynamic install/update of plexmediaserver.
[PlexRepo]
name=PlexRepo
baseurl=https://downloads.plex.tv/repo/rpm/\$basearch/
enabled=0
gpgkey=https://downloads.plex.tv/plex-keys/PlexSign.key
gpgcheck=1" > /etc/yum.repos.d/plex.repo
Importing GPG key
rpm --import https://downloads.plex.tv/plex-keys/PlexSign.key
Installing Plex Media Server
When installing with repo enabled pay attention for dependencies. They should not come from PlexRepo
yum --enablerepo=PlexRepo install plexmediaserver
Updating Plex Media Server"
yum --enablerepo=PlexRepo update plexmediaserver
Configuration
Enabling the service
systemctl enable plexmediaserver
Starting the service
systemctl start plexmediaserver
Adding firewalld services
Plex offers several options and this part just adds them to the list.
You will choose later which ones you want to enable.
firewall-cmd --permanent --new-service=plexmediaserver
firewall-cmd --permanent --service=plexmediaserver --set-short=plexmediaserver
firewall-cmd --permanent --service=plexmediaserver --set-description="Ports required by plexmediaserver."
firewall-cmd --permanent --service=plexmediaserver --add-port=32400/tcp
firewall-cmd --permanent --new-service=plexmediaserver-dlna
firewall-cmd --permanent --service=plexmediaserver-dlna --set-short=plexmediaserver-dlna
firewall-cmd --permanent --service=plexmediaserver-dlna --set-description="Enable DLNA for plexmediaserver."
firewall-cmd --permanent --service=plexmediaserver-dlna --add-port=1900/udp
firewall-cmd --permanent --service=plexmediaserver-dlna --add-port=32469/tcp
firewall-cmd --permanent --new-service=plexmediaserver-discovery
firewall-cmd --permanent --service=plexmediaserver-discovery --set-short=plexmediaserver-discovery
firewall-cmd --permanent --service=plexmediaserver-discovery --set-description="Enable local discovery for plexmediaserver."
firewall-cmd --permanent --service=plexmediaserver-discovery --add-port=5353/udp```
firewall-cmd --permanent --service=plexmediaserver-discovery --add-port=32410/udp
firewall-cmd --permanent --service=plexmediaserver-discovery --add-port=32412/udp
firewall-cmd --permanent --service=plexmediaserver-discovery --add-port=32413/udp
firewall-cmd --permanent --service=plexmediaserver-discovery --add-port=32414/udp
firewall-cmd --permanent --new-service=plexmediaserver-control
firewall-cmd --permanent --service=plexmediaserver-control --set-short=plexmediaserver-control
firewall-cmd --permanent --service=plexmediaserver-control --set-description="For controlling Plex for Roku and Plex Home Theater via Plex Companion."
firewall-cmd --permanent --service=plexmediaserver-control --add-port=3005/udp
firewall-cmd --permanent --service=plexmediaserver-control --add-port=8324/udp
Enabling firewall services for using on LAN
These rules are useful for LAN setup, they are not recommended for Interner access.
firewall-cmd --add-service=plexmediaserver --permanent
firewall-cmd --add-service=plexmediaserver-dlna --permanent
firewall-cmd --add-service=plexmediaserver-discovery --permanent
firewall-cmd --reload
firewall-cmd --list-all
Connecting the first time over localhost
Use the linked graphical guides to the final clicks. I can include it later.
Steps to take before adding library files
Setup subtitles and plugins
You should do this before you start loading meta-data as Plex will ignore it later and you will have to force it.
Disable automatic trashing of items in Plex
When you are building your library you do not want to see things disappear when you made a mistake.
Make sure you have correct access rights
Split libraries as much as it makes sense.
Plex performance drops like a stone once you have libraries with thousands of entries.
Make sure you do not have too many nested directories
Plex automatic detection gets really confused once you go more than 2 directories deep.
Finally start small, do not try to add 1400 movies at once 
Questions
DLNA or not DLNA?
You should enable it and allow it on LAN. For capable clients like VNC it is perfect. The only exception is a multi-user household where your account will be updated when you Father watches shows about cars 
SELinux compatibiliy?
There are no major issuess with SELinux
Recommended plugins?
Definitely install SRT2UTF for subtitles downloaded automatically:
https://github.com/ukdtom/SRT2UTF-8.bundle/wiki
I also recommend setting up AudioBooks in Plex:
https://github.com/macr0dev/Audiobooks.bundle
