tikz cloning graphs in background

Here is the code that did my job. I didn't need the backgrounds layer. I think just with opacity it worked out fine.

However any better solution, or improvements in my code are greatly appreciated.

\begin{tikzpicture}

    % Left Side
    \draw [line width=0.75pt](1.25,-0.25) circle (0.75cm);
    \draw [line width=0.75pt,double,double distance=5pt] (4,-1.5) -- ++(4cm,0cm) -- ++(0cm,2.5cm) -- ++(-4cm,0cm) -- cycle; 
    \draw [line width=0.75pt,double,double distance=1.5pt,->] (2.05,-0.25) -- (5.25,-0.25);
    \draw [line width=0.75pt](6,-0.25) circle (0.75cm);
    \draw [line width=0.75pt](5.25,-1.00) -- (5.25,0.50);
    \draw [line width=0.75pt](3.1,0.25) -- (2.9,-0.55);
    \draw [line width=0.75pt](2.85, -0.70) node {N};
    \draw [line width=0.75pt](2.05, 0.25) node {r};

    % Arrow

    \draw[line width=0.75pt,->,double,double distance=2pt] (9,0) -- (10.5,0.0);

    % Right Side
    \draw[line width=0.75pt] (12,0) circle (0.75cm);

    \def\recAOriginX{15.5}
    \def\recAOriginY{-0.5}
    %\draw[white,fill opacity=.75] (\recBOriginX,\recBOriginY)  -- ++(4cm,0cm) -- ++(0cm,2.5cm) -- ++(-4cm,0cm) -- cycle; 
    \draw[line width=0.75pt] (\recAOriginX,\recAOriginY)  -- ++(4cm,0cm) -- ++(0cm,2.5cm) -- ++(-4cm,0cm) -- cycle; 
    \draw[line width=0.75pt] (\recAOriginX+1.75,\recAOriginY+1.25) circle (0.75cm);

    \def\recBOriginX{15}
    \def\recBOriginY{-1.25}
    \draw[line width=0.75pt,->] (12.75,0) -- (16.55,1.0);
    \fill[white,fill opacity=.50] (\recBOriginX,\recBOriginY) rectangle (\recBOriginX+4,\recBOriginY+2.5);
    \draw[line width=0.75pt] (\recBOriginX,\recBOriginY)  -- ++(4cm,0cm) -- ++(0cm,2.5cm) -- ++(-4cm,0cm) -- cycle; 
    \draw[line width=0.75pt] (\recBOriginX+1.75,\recBOriginY+1.25) circle (0.75cm);

    \def\recCOriginX{14.5}
    \def\recCOriginY{-2.5}
    \fill[white,fill opacity=.50] (\recCOriginX,\recCOriginY) rectangle (\recCOriginX+4,\recCOriginY+2.5);
    \draw[line width=0.75pt] (\recCOriginX,\recCOriginY)  -- ++(4cm,0cm) -- ++(0cm,2.5cm) -- ++(-4cm,0cm) -- cycle; 
    \draw [line width=0.75pt](\recCOriginX+1.75,\recCOriginY+1.25) circle (0.75cm);

    \draw[line width=0.75pt,->] (12.75,0) -- (15.5,-1.05);
    \draw[line width=0.75pt,->] (12.75,0) -- (16,0.2);

\end{tikzpicture}

And here is the output

My version! =)

The result:

The code:

\documentclass{standalone}

\usepackage{tikz}
\usetikzlibrary{matrix}

\tikzset{
    base/.style = {
        , minimum width = 30mm
    }
    , my circle/.style = {
        draw
        , fill = white
        , circle
        , minimum size = 5mm
        , opacity = 0.5
    }
    , my rectangle/.style = {
        draw
        , fill = white
        , minimum width = 20mm
        , minimum height = 10mm
        , opacity = 0.5
    }
}

\begin{document}
    \begin{tikzpicture}
        \matrix (m) [matrix of nodes, nodes in empty cells, nodes = {base}] {
            & & & & \\
        };
        \node [my circle] (m-1-1-c) at (m-1-1) {} node [above right] at (m-1-1-c.45) {\tiny r};


        \node [my rectangle] (m-1-2-r) at (m-1-2) {};
        \node [my circle] (m-1-2-c) at (m-1-2) {};

        \node [my rectangle] [draw = none] (m-1-3-r) at (m-1-3) {};

        \node [my rectangle] (m-1-4-r) at (m-1-4) {};
        \node [my circle] (m-1-4-c) at (m-1-4) {};

        \foreach \i/\j in {-5/1, 0/2, 5/3}{
            \node [my rectangle, yshift  = \i mm, xshift = \i mm] (m-1-5-r-\j) at (m-1-5) {};
            \node [my circle, yshift  = \i mm, xshift = \i mm] (m-1-5-c-\j) at (m-1-5) {};
        }

        \draw [->, thick] (m-1-1-c) -- (m-1-2-c) node [midway] (n) {} node [below left] at (n) {\tiny N};
        \draw (n) -- + (0, 2mm) -- +(0, -2mm);
        \draw (m-1-2-c.west) -- + (0, 3mm) -- +(0, -3mm);

        \draw [double, thick, ->] (m-1-3-r.west) -- (m-1-3-r.east);

        \foreach \i in {1, 2, 3}{
            \draw [thick, ->] (m-1-4-c.east) -- (m-1-5-c-\i.west);
        }

    \end{tikzpicture}
\end{document}

HTH!