Big picture with several smaller ones on the side

You don't need subcaption if you have no subcaption to the images.

Here's a way, by measuring the big picture. In the example I use \scalebox just to have the big picture higher than two small ones.

\documentclass{article}

\usepackage{graphicx}

\newbox{\bigpicturebox}

\begin{document}

\begin{figure}
\centering

\sbox{\bigpicturebox}{%
  \scalebox{1}[1.2]{\includegraphics[width=.45\textwidth]{example-image}}%
}

\usebox{\bigpicturebox}\hfill
\begin{minipage}[b][\ht\bigpicturebox][s]{.45\textwidth}
\includegraphics[width=.45\textwidth]{example-image-a}\hfill
\includegraphics[width=.45\textwidth]{example-image-b}

\vfill

\includegraphics[width=.45\textwidth]{example-image-c}
\end{minipage}

\medskip
\includegraphics[width=.225\textwidth]{example-image-a}\hfill
\includegraphics[width=.225\textwidth]{example-image-b}\hfill
\includegraphics[width=.225\textwidth]{example-image-c}

\end{figure}

\end{document}

Here is a version with subcaptions; add the \label commands you need.

\documentclass{article}

\usepackage{subcaption}
\usepackage{graphicx}

\newbox{\bigpicturebox}

\begin{document}

\begin{figure}
\centering

\sbox{\bigpicturebox}{%
  \begin{subfigure}[b]{.45\textwidth}
  \scalebox{1}[1.2]{\includegraphics[width=\textwidth]{example-image}}%
\caption{Big picture}
\end{subfigure}
}

\usebox{\bigpicturebox}\hfill
\begin{minipage}[b][\ht\bigpicturebox][s]{.45\textwidth}
\begin{subfigure}{.45\textwidth}
\includegraphics[width=\textwidth]{example-image-a}
\caption{Small figure}
\end{subfigure}\hfill
\begin{subfigure}{.45\textwidth}
\includegraphics[width=\textwidth]{example-image-b}
\caption{Small figure}
\end{subfigure}

\vfill

\begin{subfigure}[b]{.45\textwidth}
\includegraphics[width=\textwidth]{example-image-c}
\caption{Small figure}
\end{subfigure}
\end{minipage}

\bigskip

\begin{subfigure}{.3\textwidth}
\includegraphics[width=\textwidth]{example-image-a}
\caption{Small figure}
\end{subfigure}\hfill
\begin{subfigure}{.3\textwidth}
\includegraphics[width=\textwidth]{example-image-b}\hfill
\caption{Small figure}
\end{subfigure}\hfill
\begin{subfigure}{.3\textwidth}
\includegraphics[width=\textwidth]{example-image-c}
\caption{Small figure}
\end{subfigure}

\end{figure}

\end{document}

This is a straightforward approach with tabular. I am shifting down the includegraphics box so that the reference is on the top margin of the figure in the first tabular. It needs a bit of manual adjusting, though --- surely it can be done better.

\documentclass{article}
\usepackage{graphicx}
\begin{document}
\begin{tabular}{@{}cc@{}}
    \raisebox{-\height}{\includegraphics[width=0.45\textwidth]{example-image-a}} & 
    \begin{tabular}[t]{@{}cc@{}}
        \raisebox{-\height}{\includegraphics[width=0.2\textwidth]{example-image-b}} & 
        \raisebox{-\height}{\includegraphics[width=0.2\textwidth]{example-image-b}} \\[1.8cm]
        \raisebox{-\height}{\includegraphics[width=0.2\textwidth]{example-image-b}} & 
    \end{tabular}
\end{tabular}

\bigskip

\begin{tabular}{@{}ccc@{}}
    \includegraphics[width=0.3\linewidth]{example-image-a} &
    \includegraphics[width=0.3\linewidth]{example-image-a} &
    \includegraphics[width=0.3\linewidth]{example-image-a} 
\end{tabular}

\end{document}