There are several extensions that allow to highlight a code snippet.
You can search for them in extensions.libreoffice.org.
Among the others
code colorizer formatter
The steps to follow are usually as easy as
Insert a new Text Box (Insert -> Text Box)
Copy and paste/write your code snippet into the text ...
For Libreofice writer use Ctrl+F10 since it does Not have a backwards P in the tool bar like Openoffice. You can also see this in the View drop down menu under "Formatting Marks" and just click to toggle it off/on
LibreOffice Writer 6.0 Guide
Reminders let you mark places in your document that you want to return
to later on, for example to add or correct information or simply mark
where you finished editing. The possible uses of reminders are limited
only by your imagination.
To set a reminder at the cursor’s current ...
Those two probably came with Microsoft Office.
Bookman Old Style is one of the Postscript base-35 fonts, so free equivalents are widely available, such as URW Bookman L and Bonum. For Papyrus, you would probably need an MS Office install disc.
I'm unsure if you want to completly disable the spell check. It is an odd document and yes there are problems with persisting the spelling vocabulary.
What you can do is choose the Base Language for the spelling check which looks like you know how to do. You can then, by going to Tools -> Options -> Language Settings -> Writing Aids, under user-...
AFAIK you can't (directly), but there are some workarounds.
Create a custom style based on "First Line Indent" (right-click on the style in the formatter window and select "New..."), so it's available among the custom styles; thus, the First Line Indent style will be available by hitting F11;
Alternatively, add the "First Line Indent" style to the Styles ...
You already have all the pieces ("Create footer" and "Insert page number").
Click just below the bottom margin, but before the end of page
Scroll down and press "+" after "Footer (Default Style)"
Press tab twice to right align text (optional)
Press "Insert" then "Page Number"
The linked page has correct steps:
"Insert - Header and Footer - Footer - (name ...
See the LibreOfffice page on how to search and replace paragraph styles such as borders. The Alternative Find & Replace for Writer extension may also be helpful.
However, you may have changed the default document template to include borders. To edit a template:
From the main menu, select File | Templates > Manage Templates.
The template with a green ...
OpenOffice (which functions identically here) has a Form Letter Guide, or LibreOffice has a Wizard to walk you through this. Choose Tools | Mail Merge Wizard | Click the Mail Merge icon on the Table Data bar to begin it. Here's a one minute video on the latter method.