Also with Vim (I can't speak for other editors) it has the option of concealing the markdown characters themselves so it looks more like a rendering of it. I don't use that personally but if you prefer not seeing the noise of backticks for code blocks or double asterisks for bold you can hide it.
If you like vim and want to use it for markdown, that's great. I personally like a more specialized tool. Then again, I'm also a writer and spend more time in that mode than most programmers. If you spend all your time programming and only occasionally need to write a markdown document, then I can see the appeal of the setup you're describing.
If you run Vim with +clipboard support then you can yank things directly to and from your system clipboard by setting `set clipboard=unnamedplus`.
Then Vim copy / pasting will work seamlessly like any other program on your system.
You can also have it seamlessly work with tmux too and even with WSL if you're using terminal Vim in Windows through WSL.
Here's a video that demos how it all works and also has a link to my dotfiles: https://nickjanetakis.com/blog/getting-copy-paste-to-work-in...
What about using your code editor's markdown plugin and real time preview in a browser?
For example with Vim, one of the plugins launches a browser and then you get a real time preview while you type in Vim. The nice thing is you can tell it to use a specific CSS file so you can get a 100% copy of GitHub's README styles. It even syncs your cursor if you want that behavior.
I demo'd the above set up here: https://nickjanetakis.com/blog/writing-and-previewing-markdo...