Making a series of child TeX files and including them as "chapters" in a parent file?

I want to build a big PDF of multiple TeX files which will all have the same preamble. They’ll have newcommand and renewcommand as well as usepackage and documentclass because each file should be standalone and compiled as a smaller PDF. But then, I want to take all of the files we have and put them in a main document. I’ve looked at the other questions:

• Include file with preamble to another tex file
• Make a .tex file that combines complete .tex documents in subdirectories
• Outsourcing TikZ code
• Manual for the standalone package on CTAN

and the standalone package. I’m not sure I’ll be able to do what I want with these.

Each child document needs to stand on it’s own, with it’s own preamble, and table of contents, etc. But they should be included in a master document with a global table of contents that ignores/copies all preambles.

Below is example code for one of the children files.

documentclass[11pt]{article}
usepackage{amsmath, amsfonts,amssymb,latexsym, multirow}
usepackage{fullpage, graphicx, subfig, float, hyperref, enumerate}
usepackage[parfill]{parskip}
usepackage{pdflscape}%for large figures
usepackage{cancel}

linespread{1.3}

hypersetup{backref,  
    pdfpagemode=FullScreen,  
    colorlinks=true}

renewcommand{dag}{^dagger}
renewcommand{d}{text{d}}
newcommand{D}{text{D}}
newcommand{bra}{langle}
newcommand{ket}{rangle}

newcommand{comment}[1]{}

newcommand{p}{partial}
newcommand{eq}[1]{begin{align*}#1end{align*}}

begin{document}

noindent fbox{
begin{minipage}{6.4in}
  medskip
  textbf{Book} hfill textbf{Author}
  begin{center}
    {Large Chapter #} [3mm]
  end{center}
today hfill Subauthor
medskip
end{minipage}
}

bigskip
tableofcontents
newpage
section{}
subsection{}
end{document}