The extra lines are probably the Markdown syntax converting existing formatting - a single line in rendered text are represented as double lines in markdown source. E.g. by default, copying html with single lines will convert to markdown, which represents them as double lines.

Try adding a shift to the paste command to paste without converting the formatting on text in the clipboard across to markdown. Or there’s a convert from HTML toggle in preferences under Editor.

Vim bindings, as far as I can tell is exactly as vim proper is - any vim cheat-sheet would get you started. However, if Obsidian has a hotkey set that collides with default vim bindings, it seems to pick at random either to do nothing or run the obsidian interface shortcut. Search your hotkeys and rebind if a vim command seems broken!

Have you tried ctrl-shft-v to paste?