General

hmmm... when i played NW, i played with sticky keys and i dont really have a problem with it, other than having to hotkey my flash jump cause i cant press the alt key in quick succession. i got him to lvl 203 before i switched back to DB.
for jump attacking, i believe i had a normal keyboard since it doesnt recognize multiple key presses, so i used sticky keys.
honestly, sticky keys isnt really that hindering, just have to get around not being able press the same key in rapid succession.. personal perspective.

The method I used to use was to enable the Spanish keyboard and put Quintiple Throw on CTRL, Jump on ALT. You then use your right ALT key to perform the attack. As you can see, this is very impractical if you're used to a more standard layout, so I just stopped playing NW altogether. A shame Nexon hasn't released a universal jump attack modifier since the class is balanced around that.

This is about Mechanical keyboards. http://www.pcgamer.com/best-mechanical-switches-for-gaming/

I have never used one before though, but there are plenty of other players around here who can tell you more about it. There are cheap gaming keyboards so it's not necessarily to buy an expensive keyboard either.

Pretty sure gaming keyboards can handle multi keys pressed down. So you can't go wrong with that, however there are many types. Read that article about each type.

I'm using a Logitech Wave Keyboard (They don't make it anymore), although it's not a (mechanical) gaming keyboards I like it and it's comfortable. It recognizes multiple key presses.

At home I have another keyboard which we bought to use for our TV. I didn't like that one, I tried it and it types like those most common keyboards on laptops. The key height are lower. It didn't recognise multiple key presses.