I think there are free editors for LaTeX that show you the code and the end result next to each other, and let you edit either.

You need to learn the ability to resist the urge to tweak layout. You're using a professional document preparation tool that well make your document look professional. Playing with trendy fonts and margins and placement is how regular people make documents in a word processor that look less professional than LaTeX.

LaTeX gives you the respectability of the corporate style of the professional science researcher, but if you want free-form do-it-how-you-like, you really really really don't want LaTeX.

YouTube. Straight up. When I learned to code my yt search history was a million different versions of "how to in python" for months. I also really liked the "Computational methods for physics" textbook (you can find the pdf for free on cambridge website), but that book is written for an audience that knows near graduate math but starts praying if their advisor asks them to write a program

For tex, i would suggest taking a basic template, and writing what you need, looking up how to do things as you need them. Theres a bunch of documentation on sites like overleaf, and you can learn a lot by looking at stackexchange threads.

Unironically -- use markdown. It's far more intuitive for most people, comes with similar git tracking benefits, and has simpler compilation / tooling steps.

Start out with Python. It's easy to learn and there are tons of courses and tutorials out there. Unless you want to be a professional programmer, it's all you'll ever need. Learning tex in this day and age is a waste of time, if you ask me.