I am not sure that I understand your question.
What you seem to request is a way to customise the default behaviour of Writer (or LO in general) so that all your preferences are active whenever you launch Writer (or other LO component).
There are two aspects:
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General LO behaviour
This is controlled by Tools>Options. Explore the various topics.
In the case of units, see libreOffice Writer>General. The Measurement unit menu allows to select the preferred unit and Tab stops defines the default evenly distributed distance between tab stops.
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Specific document preferences
They are stored in a template which is an “ordinary” document with a specific extension (.ott). It contains your customised styles and initial content. Once it is made, use File>Templates>Save as Template to save it as a template known by Writer. Once done, File>Templates>Manage Templates and right-click on your template to make it default.
Nota: If you operate under Windows, don’t create a new document directly from the desktop because this procedure never references your custom template. Open Writer first and File>New>Templates.
Since these preferences are set in principle only once, the necessity to redo the whole configuration is rather low and so is the scripting.
List numbering
If all your levels have the same formatting (i.e. same indents and tab stops), they can be set simultaneously in Format>Bullets & Numbering or Tools>Chapter Numbering (for chapter numbering) by selecting “virtual” level 1-10 instead of going through individual levels. This does not apply if indents vary with level. But, as said above, you do this only once in your custom template.
Indents
Text formatting in Writer is controlled by styles. Indents are set in paragraph styles. You use one paragraph style per “semantic category” of paragraph. E.g. nondescript paragraphs are styled with Text Body (and not be Default Style which is used to set defaults for all other styles). You can define other styles based on Text Body, changing only the attributes you’re interested in. The other attributes will be inherited from Text Body and will also inherit the changes you eventually make on Text Body without the pain of forwarding them.
There is already a built-in style First Line Indent with a pre-set 0.5cm in the first line. Customise it to your custom distance.
You then style the to-be-indented paragraphs with it. Never indent a first line with a tab.
If your question is about a whole paragraph indent, not only the first line, define your own paragraph style with the desired left indent (called Before text in the configuration dialog).
To avoid switching from keyboard to mouse and back, styles may be associated with shortcuts through Tools>Customise.
Ctrl+0 to 3 are by default assigned respectively to Text Body and `Heading 1* to Heading 3.
To discover all the possibilities, download and read the Writer Guide.
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