The fzf.vim plugin allows you to do speedy fuzzy searches for filenames and line-by-line content.

Once you've narrowed down the results and found what you're interested in, you can hit <enter> and a new buffer will open over what was already in the window. You can also open that file as a split.

Hitting Ctrl-x will open the file under the cursor as a horizontal split.

Hitting Ctrl-v will alternatively open that file as a vertical split.