Anchoring boxes for slide layouts in Tikz and Beamer

Question

I've been reading the tikz manual, and I was able to generate this MWE:

\documentclass[xcolor=dvipsnames]{beamer}
\usepackage{tikz}
\usetikzlibrary{calc, intersections,through,backgrounds,positioning}
\usepackage{pgfpages,ifthen}
\usepackage{blindtext}
\usepackage{multicol}
\usepackage{amsmath,amssymb,amsthm,mathrsfs,bbm,bm}
\usepackage{graphicx,subcaption,float,enumerate}
\usetheme[progressbar=frametitle]{metropolis}
\setbeamertemplate{frame numbering}[none]
\metroset{block=fill}
\setbeamercovered{transparent=15}

\title{Test Presentation}
\subtitle{a quick one}
\date{}
\author{}
\institute{}

\begin{document}
\maketitle

\begin{frame}
    \begin{tikzpicture}[remember picture,overlay] 
    \draw[very thick,red] (current page.west) rectangle (current
    page.south) ;
    \draw[very thick,blue] (current page.north west) rectangle (current
    page.center);
    \end{tikzpicture}
\end{frame}

\begin{frame}{A frame title}
    \begin{tikzpicture}[remember picture,overlay] 
    \draw[very thick,red] (current page.west) rectangle (current
    page.south) ;
    \draw[very thick,blue] (current page.north west) rectangle (current
    page.center);
    \end{tikzpicture}
\end{frame}


\end{document}

I'd like some help with the following:

1. How can I name the blue and red nodes, so that I can now anchor things to them later on?
2. How can I anchor these nodes to the bottom of the header? I know I need to do some calculations, and I am reading section 13.5 of the Tikz manual to figure it out. What I need to do is anchor to something like (current page.west - headerwidth), etc.
3. I would like to generate a few frames with "sample slide layouts", things like two vertical panels on the left and one long one the right, etc. Right now, I want to do this manually, and just keep a sample_slides.tex file on my computer with the code for all of these layouts that I can then just anchor new content to. Does this kind of thing make sense?

Note: I've also tagged beamer because I am sp[ecifically asking about a beamer slide header

Answer 1

For questions 1 and 2:

\documentclass[xcolor=dvipsnames]{beamer}
\usepackage{tikz}
\usetikzlibrary{calc, intersections,through,backgrounds,positioning}
\usepackage{pgfpages,ifthen}
\usepackage{blindtext}
\usepackage{multicol}
\usepackage{amsmath,amssymb,amsthm,mathrsfs,bbm,bm}
\usepackage{subcaption}
\usetheme[progressbar=frametitle]{metropolis}
\setbeamertemplate{frame numbering}[none]
\metroset{block=fill}
\setbeamercovered{transparent=15}

\title{Test Presentation}
\subtitle{a quick one}
\date{}
\author{}
\institute{}

\newlength{\test}
\makeatletter
\setlength{\test}{\totalheightof{%
  \begin{beamercolorbox}[%
      wd=\paperwidth,%
      sep=0pt,%
      leftskip=\metropolis@frametitle@padding,%
      rightskip=\metropolis@frametitle@padding,%
    ]{frametitle}%
  \metropolis@frametitlestrut@start%
  TJ%
  \nolinebreak%
  \metropolis@frametitlestrut@end%
  \end{beamercolorbox}%
}}
\addtolength{\test}{\metropolis@progressinheadfoot@linewidth}
 \makeatother

\begin{document}
\maketitle

\begin{frame}
    \begin{tikzpicture}[remember picture,overlay] 
    \draw[very thick,red] (current page.west) rectangle (current
    page.south) node (rednode) {};
        \node [above of = rednode] {test};
    \draw[very thick,blue] (current page.north west) rectangle (current
    page.center);
    \end{tikzpicture}
\end{frame}

\begin{frame}{A frame title}
    \begin{tikzpicture}[remember picture,overlay] 
    \draw[very thick,blue] (current page.north west)++(0,-\test) rectangle (current page.center);
    \end{tikzpicture}
\end{frame}


\end{document}

I am not sure if I understand your third question, but maybe https://ctan.org/pkg/gridslides is what you are looking for?

---

I have the feeling that you are asking an XY-question. If your ultimate goal is to fill these rectangles with text, I would say: don't do that - let beamer do the work for you and you will get slides that are normally perfectly aligned and and only very rarely need manual intervention. For example if you want a text block at the top and the bottom of the left hand site, you could use columns:

\documentclass{beamer}
\usetheme[progressbar=frametitle]{metropolis}

\begin{document}

\begin{frame}
    \frametitle{title}
    \begin{columns}[t]
        \begin{column}{.48\textwidth}
                Nam dui ligula, fringilla a, euismod sodales, sollicitudin vel, wisi. Morbi auctor lorem non justo. Nam lacus libero, 
        \end{column}
        \begin{column}{.48\textwidth}
                whatever should be on the right
        \end{column}        
    \end{columns}
    \vfill
    \begin{columns}[t]
        \begin{column}{.48\textwidth}
                Nam dui ligula, fringilla a, euismod sodales, sollicitudin vel, wisi. Morbi auctor lorem non justo. Nam lacus libero, 
        \end{column}
        \begin{column}{.48\textwidth}

        \end{column}        
    \end{columns}   
\end{frame}


\end{document}