The way guns scale as you level, a legendary you get will be outclassed by most blues/purples within about 5-6 levels of it. You're better off just playing the game normally, upgrading as you go. That's why farming isn't as useful for low levels.
If you need level-appropriate gear in a pinch, the golden chest in sanctuary gives decent equipment for leveling. You can find a list of the still-active golden key codes online (I know orcz.com has a pretty good list if you google it)