How do I create 'n' blank pages

You can put your "blank page recipe" into a loop, say using pgffor:

\documentclass[9pt,paper=a6,]{scrbook}
\usepackage{pgffor}

\newcommand\InsertBlankPages[1]{% \InsertBlankPages{n} => insert n blank pages
  \foreach \blank in {1,...,#1} {
    \newpage
    \thispagestyle{plain}
    \mbox{}
  }%
}

\begin{document}
  \InsertBlankPages{10}
\end{document}

Actually, the pages are not quite blank as they have a page number. If you want them truly blank then use \thispagestyle{empty}.

The expl3 function \prg_replicate:nn does what you want; its first argument is an integer n and the second argument is the code to be repeated n times.

\documentclass[9pt,paper=a6,]{scrbook}
\usepackage{xparse}

\ExplSyntaxOn
\NewDocumentCommand{\blankpages}{m}
 {
  \clearpage
  \prg_replicate:nn { #1 } { \mbox{}\thispagestyle{plain}\clearpage }
 }
\ExplSyntaxOff

\begin{document}

Notes

\blankpages{10}

Next Section

\end{document}