Question 2 above - spacing:
Somewhere is code that establishes the 45 "spacing" or perhaps whatever metric you achieved using your fill and count method.
If you wish to increase from 45 to 50 or higher then your requirement is to have less space between lines of displayed text - correct?
The applicable terminology is Leading (said as lead the metal) and Kerning.
Reference links:
https://www.templatemonster.com/blog/leading-kerning-tracking-difference/
http://www.differencebetween.net/technology/difference-between-kerning-and-leading/
You can easily find similar links.
Question 3 above - where:
What software are you using to create the text? Math software by any chance?
Photoshop permits such configuration:
https://helpx.adobe.com/photoshop/using/line-character-spacing.html
You may or may not be able to configure the Leading depending on the software that you are using.
And if there is some way to configure the Leading then that would be a user configurable setting in the software and likely limited to some range or perhaps fixed increments such as 45, 50, 55, and 60.
The other aspect of it all is that your measurements could be hardware constrained by the console. There are only so many pixels and trying to change the spacing may be limited. You cannot get the lines closer together because there are no more "rows" of pixels that can be used for text and not Leading.
Debian Bullseye
Interestingly enough and coincidentally I came across the following link:
https://www.debian.org/releases/bullseye/mips64el/release-notes.en.pdf
I am not an "Open Source" person/follower per se so I truly (full disclosure) do not know if the .pdf will be of much help.
However, you may be able to note something that provides an applicable idea or hint.
Or someone else may be able to offer further ideas and suggestions. I have no problem with that.