No offence intended but you won't go nowhere with the material you provided.
The first thing to learn with Writer is styles.
Start with paragraph styles. Presently all your text except headings are in First Line Indent (which makes no sense) and you use empty such paragraph to get vertical spacing. Writer is more powerful than a mechanical typewriter and this power allows you to care only for your text without thinking of formatting. All can be done automatically once you have designed or tuned your paragraph styles.
Download and read the Writer Guide for the basis.
The chore of your question is "how to translate part structuring into Writer concepts"?
Every time you need a part of a document which should be laid out with different margins, header/footer, type of page numbering, … i.e. a different page design, this calls for a different page style. Transition from a page style to the next is done with a special page break you configure with Insert>More Breaks>Manual Break, not the simple Ctrl+Enter which simply goes to the next page within the same part (same page style).
If the page style change occurs always in the same context (e.g. at chapter start), this special page break can be incorporated in the paragraph style. Merely styling the paragraph (heading) with the adequate style will automatically add the page break.
I don't know how large your final document will be. Even if it reaches ~500 pages, don't bother yourself with a master document and included sub-documents. You seem to be a newbie (again, no offence untended) and there are subtle problems with masters. Don't confront them until you're familiar enough with styles and cross-references (useful to give links to parts of your document).
Learn by small steps otherwise you'll throw away Writer, pretending it's scrap because you don't understand the underlying concepts. (It looks like you've already messed up built-in paragraph styles and you've added character styles which betray your ignorance about their function -- Default Paragraph Font and fontstyle01, not to speak of your LaTex family).
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