Is this what you expect ?
Only one page
More than one page, Contact info only in the last page.
You requested a template and gave some guidelines, with a graphic example. That means it will be used multiple times, with different content.
Therefore, the designer must allow changes to the content data provided, in addition to some minor changes to the graphic design, and desirably empower the end user to perform the final fine-tuning without further consulting with experts.
I found that xcoffin is the best option for these cases. It emulates a graphic design program: it puts the stuff (text, tables, figures, etc) into specials boxes and then join the boxes using predefined points of the boxes like [l,t] (left top corner and so on) plus adding X and Y offsets as needed.
The important points are that (1) the assembly is done using the relative positions of the boxes with respect each other and (2) the graphic design its separated from the content, thus changes in one does not alter the other.
xcoffin itself was design with simplicity in mind. There are few commands and it is easy to learn. Just follow the example.
https://ctan.org/pkg/xcoffins?lang=en
The header is composed by five boxes: 2 lines, two rectangles and the title. All will collected by a frame using their relative positions
The footer uses four boxes, a rule, a figure, the contact data and the address data. Again they will collected in a frame.
The first task is filling the boxes with the content. The text part it is done like any LaTeX paragraph. Other boxes include figures or more complex objects.
I choose to add the rectangles using tcolorbox because it is easy to set up the rectangles or comment or change some specs by the end user, and also because it provides the transparency required.
To allow for maximum use of the pages I included geometry. Note that the header and the footer extend 10mm towards the margins while the text is narrower and centered.
Instead of typing the content of the proposal into the template it will be best write it in a separate file,
from Background to Requirements, and then input the file with, lets say, \input{proposal2021.tex}.
This is the code
\documentclass[11pt]{article}
\usepackage[left=30.0mm, right=30.0mm, top=20mm, bottom=20mm, headheight=45mm, footskip= 12mm, headsep=6mm, marginparsep=0mm]{geometry}
\usepackage{graphicx}
\usepackage{xcoffins,calc,xcolor} % added
\usepackage{kantlipsum} % dummy text
%\usepackage{showframe} %added for testing page geometry
%\renewcommand*\ShowFrameColor{\color{red}} %added
\usepackage[many]{tcolorbox}
\NewCoffin\Hframex
\NewCoffin\Hthickrulex
\NewCoffin\Hthinrulex
\NewCoffin\HDarkGreenx
\NewCoffin\HLightGreenx
\NewCoffin\HTextx
\NewCoffin\Fframex
\NewCoffin\Flogox
\NewCoffin\Fleftx
\NewCoffin\Fcenterx
\begin{document}
%% Filling the header boxes
\SetHorizontalCoffin\Hframex{\rule{\textwidth+20mm}{0mm}} % collector frame for header
\SetHorizontalCoffin\Hthickrulex{\rule{\textwidth+20mm}{1.5mm}} % header upper rule
\SetHorizontalCoffin\Hthinrulex{\rule{\textwidth+20mm}{0.5pt}} % header lower rule
\SetVerticalCoffin\HTextx{\textwidth}{% Title
\color{white}\fontsize{20pt}{24pt}\selectfont
\centering\bfseries\sffamily\noindent
Research Project title \medskip\\
\fontsize{14pt}{18pt}\selectfont
(Proposal for a master Project) \medskip \\
WS2020/21
}
\SetHorizontalCoffin\HDarkGreenx{% Back darker green rectangle
\begin{tcolorbox}[
width=\textwidth+10mm,
arc=4pt,
height=9em,
boxsep=0cm,
toprule=0.2pt,
leftrule=0.2pt,
bottomrule=0.2pt,
rightrule=0.2pt,
colback=green!55!blue!70,
colframe=green]
\end{tcolorbox}%
}
\SetHorizontalCoffin\HLightGreenx{% light green transparent rectangle
\begin{tcolorbox}[
width=\textwidth+10mm,
arc=1mm,
height=9em,
boxsep=0cm,
toprule=0.2pt,
leftrule=0.2pt,
bottomrule=0.2pt,
rightrule=0.2pt,
colback=green!45,
colframe=green,
breakable,
enhanced jigsaw,
% opacityframe=0.4,
opacityback=0.2,]
\end{tcolorbox}
}
% Filling the footer boxes
\SetHorizontalCoffin\Flogox{% a figure, logo , etc
\includegraphics[height=70pt,width=70pt]{example-grid-100x100pt}
}
\SetHorizontalCoffin\Fframex{\rule{\textwidth+10mm}{0pt}} % collector frame for footer
\SetVerticalCoffin\Fleftx{0.3\textwidth}{% Contact left side
\sffamily\fontsize{8pt}{10pt}\selectfont\noindent
\textbf{\large Contact}\smallskip\\
\textbf{RESEARCH GROUP IT--ENTREPRENEURSHIP}\\
Prof. Dr. \\
\\
\begin{tabular}{@{}ll}
\textbf{Email} & rsgit@gmail.com \\
\textbf{Website }& www.rsgit.com \\
\textbf{Phone} & +49 (0) 4236 0927 \\
\textbf{Twitter} & twitter.com/rsgit
\end{tabular}
}
\SetVerticalCoffin\Fcenterx{0.3\textwidth}{% {% Contact centre
\sffamily\fontsize{8pt}{10pt}\selectfont\noindent
\textbf{\large Address}\smallskip\\
\textbf{Institute}\\
Digital Engineering Department, \\
University of \\ Research Group IT--Entrepreneurship\\
Campus III Building G-1 \\
Rodolf Str. 162--184 \\
Germany
}
% Asembly of the header five boxes to \Hframex
\JoinCoffins*\Hframex[l,t]\Hthickrulex[l,t](-5mm,14mm) % (X, Y) offsets
\JoinCoffins*\Hframex[l,t]\HDarkGreenx[l,t](5mm,10mm)
\JoinCoffins*\Hframex[l,t]\HLightGreenx[l,t](-5mm,3mm)
\JoinCoffins*\Hframex[l,t]\HTextx[l,t](0mm,-1mm)
\JoinCoffins*\Hframex[l,t]\Hthinrulex[l,t](-5mm,-34mm)
% Assemply of the footer four boxes to \Fframex
\JoinCoffins*\Fframex[l,t]\Hthinrulex[l,t](-5mm,3mm) % (X, Y) offsets
\JoinCoffins\Fframex[l,t]\Fleftx[l,t](-5mm,0mm)
\JoinCoffins\Fframex[hc,t]\Fcenterx[l,t](-10mm,0mm)
\JoinCoffins\Fframex[r,t]\Flogox[r,t](5mm,0mm)
% Put the assembled header on the top of the page, typeset and add space
\noindent\TypesetCoffin\Hframex(-5mm,0mm)\vspace*{35mm}
%%%%%%%%%%%%%%%%%%%%
%%% Document starts here <<<<
%
%%% Perhaps input the data from another file with \input{proposal2021.tex}
%
\section{Background}
1.2 \kant[1-2]
\section{Objetives}
4.7 \kant[4-7]
\section{Deliverables}
7.11 \kant[7-11]
\section{Requirements}
12.14 \kant[12-14]
%% Document ends here <<<<
%%%%%%%%%%%%%%%%%%%%
% Put the assembled footer at the bottom and typeset
\vfill
\noindent\TypesetCoffin\Fframex(-10mm,0mm)
\end{document}
