New to LaTeX and some questions about a template.

I never used LaTeX before and was looking into it for my bachelor thesis.
My faculty is offering a LaTeX template but I don't know if I did anything wrong while compiling it or if the template is just bad.

Here are the points I am wondering about:

1. first page is empty with page number, where does that come from? (solved)

2. empty pages (\input{leereSeite}) missing, for example between "Titelseite" and "Erklärung" (solved)

3. the ... above (Datum) and (Unterschrift des Studierenden) in "Erklärung" aren't the same length and position as the text (solved)

4. while compiling I get "Underfull \hbox (badness 10000)" 3 times and "Underfull \hbox (badness 2980)" once, is this bad? (solved)

Thanks in advance for any help!

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