Document Blending: An Analysis of the Sex Appeal of Business Instruments

Question

Here is what I'm working with so far:

\documentclass{letter}
\usepackage{background}
\usepackage{lipsum}
\backgroundsetup{%
  scale=4,       %% change accordingly
  angle=0,       %% change accordingly
  opacity=.1,    %% change accordingly
  color =green,  %% change accordingly
  contents={\begin{tikzpicture}[remember picture,overlay]
        \node at ([yshift=11pt,xshift=5pt]current page.center) {\includegraphics[width=5cm]{example-image-a}};
    \end{tikzpicture}}
}
\usepackage{invoice}
\address{\emph{Invoice from:} \\ My Address \\ My Address \\ My Address}
\signature{Elmo Face}
\date{23. May 2009}
\begin{document}
  \begin{letter}{\emph{Invoice to:} \\ Your Address \\ Your Address \\ Your Address}
    \opening{Invoice no. 1}
    My greeting \footnote{Super important, so don't forget.}
    \begin{invoice}{USD}{0}
      \ProjectTitle{Example Project}
      \Fee{Development} {1000.00} {1}
    \end{invoice}
    \closing{Invoice Release Authorization}
  \end{letter}
\end{document}

I'd like to have the comment box here, but I don't know how to get stackengine:

\documentclass{letter}
\usepackage[usestackEOL]{stackengine}
\edef\tmpbs{\the\baselineskip}
\setstackgap{L}{\tmpbs}
\newlength\tmpwd
\newlength\tmpht
\usepackage{invoice}
\fboxrule=1pt

\let\svaddress\address
\renewcommand\address[2][]{ OPTIONAL ARGUMENT AS [~] FOR EMPTY INVOICE BOX
  \ifx\relax#1\relax\svaddress{#2}\else
  \def\theaddress{#2}\invoicenote{#1}\fi}

\def\invoicenote#1{
  \def\stackalignment{l}
  \setbox0=\hbox{\expandafter\Longstack\expandafter{\theaddress}}
  \tmpwd=\wd0\relax
  \tmpht=\ht0\relax
  \def\y{\fboxsep=0pt\fbox{\rule{0pt}{\tmpht}
    \stackon[\tmpht-\tmpbs]{\rule{\dimexpr\textwidth-\tmpwd-3cm\relax}{0pt}}
    {~\textsf{\strut INVOICE}~~\smash{\Longunderstack{#1}}}}}
  \svaddress{\llap{\y\hspace{3cm}}\expandafter\Longstack\expandafter{\theaddress}}
}

  ANY OF THESE FORMS WILL WORK:
\address{\emph{Invoice from:} \\ My Address \\ My Address \\ My Address}
\address[~]{\emph{Invoice from:} \\ My Address \\ My Address \\ My Address}
\address[Hi, Joe\\ Here is your order]{\emph{Invoice from:} \\ My Address \\ My Address \\ My Address}

\signature{Piglet Master}
\date{23. May 2009}
\begin{document}
  \begin{letter}{\emph{Invoice to:} \\ Your Address \\ Your Address \\ Your Address}
    \opening{Invoice no. 1}
    My greeting \footnote{I am a man.}
    \begin{invoice}{Euro}{0}
      \ProjectTitle{Example Project}
      \Fee{Development} {1000.00} {1}
    \end{invoice}
    \closing{Invoice Release Authorization}
  \end{letter}
\end{document}

Starting with what I've got so far---in addition to this comment-boxed version, I'd like to blend it with some of the elements of the following---which I'll explain below the image:

I want the "Thank you for your business." slogan at the very bottom---like 1.5cm above the bottom of the page (centered) and a comment box right above the "Invoice Release Authorization" text that has a width, but dynamic height, that is the same as the lines separating the invoice. Also, I need a big QR code that encodes my invoice number that has an edge length the same length as the line above the footnote.

---

I'm also having trouble with aligning the watermark. It's not centered, and why is it that whole document seems shifted down so low below the top of the page?

---