Zeilenabstand und Schriftgröße

\documentclass[liststotoc,headsepline, footsepline,numbers=noendperiod]{scrreprt}
\RequirePackage[l2tabu, orthodox]{nag}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[american,ngerman]{babel}
\usepackage{csquotes}
\usepackage[backend=biber,style=authoryear]{biblatex}
\usepackage{graphicx}
\usepackage{fancyhdr}
\usepackage[german]{fancyref}
\usepackage[margin=3cm, right=2cm]{geometry}
\usepackage{appendix}
\usepackage[final]{pdfpages}
\usepackage{float}
\usepackage{lscape}
\usepackage{eurosym}
\usepackage{setspace}
\usepackage[printonlyused]{acronym}
\usepackage[format=plain,justification=centering,singlelinecheck=off]{caption}
\usepackage[multiple]{footmisc}
\usepackage{titlesec} 
\usepackage[]{url}
\usepackage{arydshln}
\usepackage{enumitem}
\usepackage{color}
\definecolor{dunkelgrau}{rgb}{0.8,0.8,0.8}
\definecolor{hellgrau}{rgb}{0.95,0.95,0.95}
\usepackage{colortbl}
\usepackage[bookmarksopen,colorlinks=true]{hyperref}
\hypersetup{citecolor={blue}}
\hypersetup{citebordercolor={1 1 1}}
\hypersetup{linkcolor={blue}}
\hypersetup{linkbordercolor={1 1 1}}

\usepackage{amsfonts}   
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{blindtext}