How to change default image fit in border preserve ratio

My questions are always about how to permanently alter the default template to a useful standard. This is always difficult in LibreOffice Writer.
If we prefer not to use multiple templates, but would like one basic one for all writing, saving articles, etc. Potentially for the classroom, to save a lot of texts from magazine/ blog/ journal websites. (During years of MS Office use it had become quite simple to copy the selected text and photographs and drop them into a document, making minor adjustments if necessary.)
With LibreOffice Writer, I cannot yet do this; to force a document to keep images inside the text boundaries and not overlap the margins or the text below it, or the header. To decipher all the parameters in the dialogue boxes to achieve this. [Ex: I follow the manual instructions, and end up with an image that is inside the text boundaries (at last!) but elongated. Undo, start again. For each of three or four images, it becomes very time-consuming.]

((Even the multiple predetermined fonts the software forces for a multitude of categories is dizzying. If I want the title in a larger, bolder font, that would be quite simple to do for myself, rather than having to alter the categories of every font style to my desired standard, one by one, in every document. It is a ton of work to undo all the software settings, and to not find them set as I want them when I return to the default template again))

Hoping to find a simple method to set all photos to paste automatically this way, with occasional adjustments to be made, rather than wrestling with every image, sometimes multiple images that ought to be handled in the same standard way. And to do this in a blank template document, prior to any images being inserted.

(Trying very hard to learn! But terribly nervous that with a school year coming, I may be forced to try to reacquire the dreaded MSOffice unless I can have a usable, easy-to-work-with template.)
Thanks VERY much in advance for any help you can provide.

Upgrade to LibreOffice 6.4.6. A recent version of LO changed the default for pasting pictures to Anchor as Character. This means the picture will remain within the text area. To size smaller, grab a corner handle and resize with mouse, the picture will keep its ratio. (I would normally advise using Insert > Image.. to avoid excessive file size, at least for jpg)

I don’t understand about multiple predetermined fonts. On a new document there are just two fonts in all the styles: Liberation Serif (for body text) and Liberation Sans (for Headings). They are different sizes to help the reader know the levels.

All the styles inherit from the Default Style so if you don’t like Liberation Serif then open a new document, open the Styles sidebar (F11), right-click on Default Style and select Modify, in the Font tab change it to something more to your liking. To change the headings, right-click on Heading, select Modify, in the Font tab change it, OK. All your body text and Headings have had the font changed. Save as a template: File > Templates > Save As Template... , when you are happy you can even make it the default.

Best to know more, download and read the sections you are unsure about in Writer Guide from LibreOffice site

A much better way to customise the base fonts so that the change is permanent and valid four all future documents is to Tools>Options, LibreOffice Writer>Basic Fonts (Westen). Default Style paragraph style inherits from these options, provided it has not be modified (in which case your modifications override the options).

@bwp123: download the Writer Guide and read the chapters about styles. They will really save your life: reformatting is a double-click operation when your styles are finalised. BUT, if your documents come from Word, you’ll bump into big compatibility problems because both suites are based on different principles (styles are much less developed in Word then in Writer which causes the creation of many many manual “single-shot” formatting you must correct individually).