The installation took only a few minutes and then I was able to set up the Bitcoin Core to sync that took ~30h for finish.
After that I was also able to install electrs and synchronize, process that took only a few hours.
The only question I have is after installing and fully synchronizing Bitcoin Core + Electrs, is it expected to occupy approximately 875GB of disk space ?
Successfully installed Start9 OSv0.3.5~1 on a Thinkpad P53. Process was really straightforward. Lower resource usage and better temperatures than in my previous setup on Debian on the same laptop( on stock Debian I had to undervolt the processor to keep temps low lol). I have just noticed that when the lid is closed fans go crazy but I have seen other topics about that. I will try those solutions and edit this post if the problem is solved.