Figure preceded by small text, long caption on next page

Question

I have a figure caption that is too long to fit in the same page of the image. I would like to precede the image with a little bit of text and start the next page by the caption, then followed by text as in this picture:

(I'm using sections because I need the figure to not be sent too far from Section 1)

Here is the code of the closest I could get to it:

\documentclass{article}
\usepackage[a4paper]{geometry}
\usepackage[english]{babel}
\usepackage{caption}
\usepackage{afterpage}
\usepackage{environ}
\usepackage{mwe}

\newsavebox{\doublepagecaption}
\newsavebox{\doublepageimage}

\NewEnviron{doublepagefigure}[2][]% #1=short caption (optional), #2=caption
{\global\setbox\doublepagecaption=\hbox{%
  \parbox{\textwidth}{\captionof{figure}[#1]{#2}}}%
 \global\setbox\doublepageimage=\hbox{\parbox{\textwidth}{\BODY}}%
 \afterpage{
 \ifodd\value{page}%
   \afterpage{%
    \vspace*{\fill}\vspace{-\baselineskip}%
    \noindent\usebox{\doublepageimage}\vfill\pagebreak
    \begin{figure}[b]\usebox{\doublepagecaption}\end{figure}}%
 \else
   \vspace*{\fill}\vspace{-\baselineskip}%
   \noindent\usebox{\doublepageimage}\vfill\pagebreak
   \begin{figure}[b]\usebox{\doublepagecaption}\end{figure}%
 \fi}}

\renewcommand{\bottomfraction}{0.5}% fraction of page allowed for bottom floats

\begin{document}

\section{Section 1}

\lipsum[1]

\begin{doublepagefigure}[(Caption next page.)]{\textbf{\lipsum[2-3]}\label{fig:test1}}
\centering{
\begin{subfigure}
    \caption{vero eos et accusamus et}\label{subfig1}
    \includegraphics[width=0.3\linewidth]{example-image}
\end{subfigure}
\begin{subfigure}
    \caption{vero eos et accusamus et}\label{subfig2}
    \includegraphics[width=0.3\linewidth]{example-image}
\end{subfigure}
\begin{subfigure}
    \caption{vero eos et accusamus et}\label{subfig3}
    \includegraphics[width=0.3\linewidth]{example-image}
\end{subfigure}
\begin{subfigure}
    \caption{vero eos et accusamus et}\label{subfig4}
    \includegraphics[width=0.3\linewidth]{example-image}
\end{subfigure}
\begin{subfigure}
    \caption{vero eos et accusamus et}\label{subfig5}
    \includegraphics[width=0.3\linewidth]{example-image}
\end{subfigure}
\begin{subfigure}
    \caption{vero eos et accusamus et}\label{subfig6}
    \includegraphics[width=0.3\linewidth]{example-image}
\end{subfigure}
\begin{subfigure}
    \caption{vero eos et accusamus et}\label{subfig7}
    \includegraphics[width=0.3\linewidth]{example-image}
\end{subfigure}
\begin{subfigure}
    \caption{vero eos et accusamus et}\label{subfig8}
    \includegraphics[width=0.3\linewidth]{example-image}
\end{subfigure}
\begin{subfigure}
    \caption{vero eos et accusamus et}\label{subfig9}
    \includegraphics[width=0.3\linewidth]{example-image}
\end{subfigure}
}
\end{doublepagefigure}


\lipsum[4-7]

\section{Section 2}

\lipsum[8-10]

\end{document}

using the code from John (Figure on an even page and caption on the following page), and here is what I get:

Problems I can't solve:

(1) the subfigures come out clustered,

(2) captions of the subfigures don't come out,

(3) the caption is at the bottom of the next page instead of top (comes from \renewcommand{\bottomfraction}{0.5} but "topfraction" or a lower fraction will push the caption to a 4th page),

(4) there is no text above the figure,

(5) I don't necessarily need the figure to be on an even page.

How can it be done properly?

Answer 1

Just to show how to make the code work for your example. Note that the subcaption package requires a width argument for subfigure (and \def\@captype{figure}). OTOH, one no longer needs to use the caption package (no \captionof).

Also, the short caption is intended for the \listoffigures.

\documentclass{article}
\usepackage[a4paper]{geometry}
\usepackage[english]{babel}
\usepackage{subcaption}
\usepackage{afterpage}
\usepackage{environ}
\usepackage{mwe}

\newsavebox{\doublepagecaption}
\newsavebox{\doublepageimage}
\makeatletter
\NewEnviron{doublepagefigure}[2][]% #1=short caption (optional), #2=caption
{\def\@captype{figure}%
 \global\setbox\doublepagecaption=\vbox{\caption[#1]{#2}}%
 \global\setbox\doublepageimage=\vbox{\BODY}%
 \afterpage{%
 \ifodd\value{page}%
   \afterpage{%
    \vspace*{\fill}\vspace{-\baselineskip}%
    \noindent\usebox{\doublepageimage}\vfill\pagebreak
    \begin{figure}[t]\usebox{\doublepagecaption}\end{figure}}%
 \else
   \vspace*{\fill}\vspace{-\baselineskip}%
   \noindent\usebox{\doublepageimage}\vfill\pagebreak
   \begin{figure}[t]\usebox{\doublepagecaption}\end{figure}%
 \fi}}
\makeatother

\renewcommand{\bottomfraction}{0.5}% fraction of page allowed for bottom floats

\begin{document}

\section{Section 1}

\lipsum[1]

\begin{doublepagefigure}[(Caption next page.)]{\textbf{\lipsum[2-3]}\label{fig:test1}}
\centering
\begin{subfigure}{0.3\textwidth}
    \caption{vero eos et accusamus et}\label{subfig1}
    \includegraphics[width=\linewidth]{example-image}
\end{subfigure}
\begin{subfigure}{0.3\textwidth}
    \caption{vero eos et accusamus et}\label{subfig2}
    \includegraphics[width=\linewidth]{example-image}
\end{subfigure}
\begin{subfigure}{0.3\textwidth}
    \caption{vero eos et accusamus et}\label{subfig3}
    \includegraphics[width=\linewidth]{example-image}
\end{subfigure}
\begin{subfigure}{0.3\textwidth}
    \caption{vero eos et accusamus et}\label{subfig4}
    \includegraphics[width=\linewidth]{example-image}
\end{subfigure}
\begin{subfigure}{0.3\textwidth}
    \caption{vero eos et accusamus et}\label{subfig5}
    \includegraphics[width=\linewidth]{example-image}
\end{subfigure}
\begin{subfigure}{0.3\textwidth}
    \caption{vero eos et accusamus et}\label{subfig6}
    \includegraphics[width=\linewidth]{example-image}
\end{subfigure}
\begin{subfigure}{0.3\textwidth}
    \caption{vero eos et accusamus et}\label{subfig7}
    \includegraphics[width=\linewidth]{example-image}
\end{subfigure}
\begin{subfigure}{0.3\textwidth}
    \caption{vero eos et accusamus et}\label{subfig8}
    \includegraphics[width=\linewidth]{example-image}
\end{subfigure}
\begin{subfigure}{0.3\textwidth}
    \caption{vero eos et accusamus et}\label{subfig9}
    \includegraphics[width=\linewidth]{example-image}
\end{subfigure}
\end{doublepagefigure}


\lipsum[4-7]

\section{Section 2}

\lipsum[8-10]

\end{document}