Config is ok maybe try adding an on demand scanner and anti-virus. You should also edit your title. For example to follow the rules you should change the name to, Above's Security Config.
Your config is good enough for me. No need to add an antivirus, yet you may consider adding some on-demand scanners.
A secondary browser should be added just in case..
Why use Adblock forYouTube while your Firefox already have Adguard?
The antivirus on Linux today is necessary and is no longer science fiction. An AV for Linux desktop is not very heavy.
It has an impact on Linux server where an AV is pretty much essential to detect suspicious files.
You may add Time Machine program to capture snapshots on your system to revert any changes. Other thanthat considering your on Linux hence you're free from threats in majority.
He is on Linux... you have less than 50 malwares that are considered as serious threats.
On Linux , AV are even worse than on Windows; better use the applocking feature than Linux provides.
Your config is good enough for me. No need to add an antivirus, yet you may consider adding some on-demand scanners.
A secondary browser should be added just in case..
Why use Adblock forYouTube while your Firefox already have Adguard?
Good config. I would only recommend a AV scanner if you have other machines in the house running windows on the same network and if you intend to transfer files back n forth with them. Other then this, as @Umbra mention using "Mandatory Access Control" is the way to go. Here is a starting point, Apparmor is built into Ubuntu.