Sounds you might want to use "tagbar"? https://github.com/majutsushi/tagbar
First of all, I prefer to have less on my screen, not more. I believe that the less visual clutter you have on the screen the better you feel and the more productive you are.
Second, activating tagbar adds a bar on the right. That means my code window will shrink. But my code window is exactly the size I like it.
Third, I would have to trust those many thousands of lines of code by "someone from the internet".
Completely agree on this one. I'd probably prefer it if you can toggle between tagbar's view and your code (there may or may not be a way to do that, I didn't look at the docs).
> Third, I would have to trust those many thousands of lines of code by "someone from the internet".
This is true, but then again, you're already trusting vim, Linux and millions of lines of code all around you ;) It all comes down to trade-offs at the end of the day.