Questions[latex](ubuntu)

I'm running Ubuntu 20.04. I installed TexStudio via aptitude. But when I try to build a document, I get in TexStudio the following error:

File `letltxmacro.sty' not found. \RequirePackage{letltxmacro}[2008/06/13]

After some Google search, I found that it may belong to the packages gl2ps or libgl2ps*. However, neither of them is available in my repository:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package gl2ps

Is it possible to fix this? If yes, how?

I would like to know how to properly install, and use texlive along with the package manager tlmgr in Ubuntu. Here is what I did to install texlive:

sudo apt-get install texlive-latex-base texlive-latex-extra texlive-latex-recommended

And now I do have texlive, but the package manager is not working. Following is the error

sudo tlmgr update -all
(running on Debian, switching to user mode!)
cannot setup TLPDB in /home/kniwor/texmf at /usr/bin/tlmgr line 5336.

Is there a better way to install texlive? What can I do to fix the package manager at this point?

Using the terminal in Debian/Ubuntu, how does find the version of the system's TeX Live distribution? I don't have tlmgr so I would need to need to do this either through apt-get, aptitude, or some command that invokes the --version flag. Thanks.

How to check if a LaTeX package has been installed in Ubuntu?

When installing, I followed the methods mentioned in math.arizona.edu and n.wikibooks.org.

I'd like to learn and use LaTeX on Ubuntu. What packages do I need? What is the best editor for LaTeX code on Ubuntu for a new LaTeX user? I'd also like the ability to see the code in one pane and the results in a second pane, if possible -- not necessarily WYSIWYG, though.