Change appearance of footnotes

Question

I need to change the appearance of footnotes in a document that uses the book class. In the document, I am using a custom TrueType font that is scalable and can do half-point sizes, e.g., 10.5 pt, which is the normal size of the text in my document. Here is what I need to do:

1. Change the size of the footnote text to 8.5 pt (or a substitute as close as possible).
2. Also change the size of the number before the footnote text (but not the mark in the main text) to 8.5 pt and remove superscript formatting.
3. Remove the paragraph-like indentation.
4. Have a hanging indentation such that the text of a possible second line of text is aligned horizontally with the start of the first line, just like in this enumeration here.
5. The horizontal space between the number and the text should be small (i.e., not like the hang option in the footmisc package).
6. Have about 5 mm horizontal space to the left before the footnote number starts.

I would also be happy to receive answers about a subset of these points if you cannot answer all of them.

Here is a screenshot of the Word template I am trying to imitate:

I am aware that the default footnote style looks better. But this is what my publisher is requesting. Thanks in advance for any hints.

Answer 1

Since in the comments you said that using KOMA-Script is a possible alternative for you: if you use

\documentclass[fontsize=10.5]{scrartcl}

(or with scrbook…) then the footnote size already is quite close to what you want: 8.75pt. The other requirements depend a bit on the »Have about 5 mm horizontal space to the left before the footnote number starts«. If we assume the footnote number plus the space between number and text to have about 7.5pt of horizontal space ({\footnotesize\setbox0\hbox{1~}\the\wd0} confirms this) then

\deffootnote[\dimexpr5mm+7.5pt\relax]{\dimexpr5mm+7.5pt\relax}{1em}{\thefootnotemark~}

should fit your needs:

\documentclass[fontsize=10.5]{scrartcl}
\usepackage[T1]{fontenc}
\usepackage{lmodern}

\deffootnote[\dimexpr5mm+7.5pt\relax]{\dimexpr5mm+7.5pt\relax}{1em}{\thefootnotemark~}

\begin{document}

\null\vfill

\noindent Text with a footnote\footnote{Footnote text that spans more than one
  line. Need still some more to fulfill this requirement. And still some
  more.}.
Text with a footnote\footnote{Footnote text that spans more than one
  line. Need still some more to fulfill this requirement. And still some
  more.}.
\end{document}