You could use the baposter
class.
You can adjust the fontscale
option until you are happy with the font sizes.
MWE
(Don't you love the default colours?)
\documentclass[paperwidth=96in,paperheight=48in,landscape,fontscale=0.2]{baposter}
\usepackage{lipsum}
\begin{document}
\begin{poster}{
headershape=rectangle,
headerborder=closed,
textborder=rectangle,
}{}{Poster Title}{Poster Author}
\headerbox{Highlighted box}{name=box1}{\lipsum[1-2]}
\headerbox{Highlighted box}{below=box1}{%
\tiny tiny\par
\scriptsize scriptsize\par
\footnotesize footnotesize\par
\small small\par
\normalsize normalsize\par
\large large\par
\Large Large\par
\LARGE LARGE\par
\Huge Huge\par
}
\headerbox{Highlighted box}{column=1}{\lipsum[3-4]}
\headerbox{Highlighted box}{column=2}{\lipsum[4-5]}
\headerbox{Highlighted box}{column=3}{\lipsum[6-7]}
\end{poster}
\end{document}

baposter
.