there is some ways to solve this, one is not creating this kind of files, not recommended, another way is changing the path are this is saved, setting `backup-directory-alist` and `auto-save-file-name-transforms` you can change where this files is stored, you can also use no-litterring to this.

to use asap emacs to programming, you will only need a lsp frontend, for example, eglot is now a built-in package, or lsp-mode, another lsp for emacs, if you configurate this package, you have a minimal ide on emacs.

Then when you have time, you can search about a completion frontend, like company or corfu, then a theme for emacs, like modus-themes or doom-theme, then you can use a minibuffer ui, like vertico, ivy or helm and to use git, the package is magit.

When you are familiar to emacs, you can see thing like, completion-at-point-functions, `completion-styles and begin to customizing emacs to your liking.

as you said, display-line-numbers do the shift when the cursor change the quantity of numbers in the line, from 9 to 10, for example, maybe if you use `absolute` can help, or you use can try change a fixed width from the line number, so it cannot change the window size.

Also, you can see this example from modus-theme to help you.

using the Modus-Theme, you can disable this features and customize all visual aspects of emacs