I haven't used the PnP kits, so I'm not 100% sure, but I think that's all you will need. You may need to solder the LED to the LED leads. The kit has the quick connects on it, and your warrior LED may not. That's not a hard thing to do, but if you don't have solder, or an iron then you might as well just buy a PnP LED too. Youd end up spending almost as much on the stuff you'd need to do a good solder job.
As for the board differences, the viridian font is more of a "light side" font. It sounds a little closer to the classic saber sounds from the movies and features a blaster block effect when you hit the switch (sounds like an AT-AT firing). The crimson is more the "dark side" font. It's has a little deeper growl to it and the button effect is force lightning.
I have a bastion with the viridian font in it and it sounds fantastic in that hilt.