LED's definitely require current limiting - you need to use a controlled current supply.
You can wire as many LED's in series as you want/can supply voltage for (each LED forward voltage, added up) / can supply safely with enough voltage (don't want people being fried with 400 volts!). If one LED wants 500mA at 4V, then ten in series will need 500mA at 40V.
Don't wire LED's in parallel without serious thought. Each one will vary slightly in the forward voltage with a given current - the effect being that they will share current unequally. That can cause the harder-driven one to eventually overheat (as the LED warms up, its forward voltage drops, get more current, gets hotter...) You might get away with it, or you might not. With a lot of expensive LED's, I would not risk it. Drive each series LED string with its own regulated current, or use a current mirror. See here: **broken link removed**