For connecting to the beta server, yes, you just need the pk3 files here: http://www.shadowspawn.net/game-files/wfa/, just the pk3 files. That's all that's on the beta server (for now). The three-wave are on there because I was doing map experiments with the bots, but it's not part of wfa, I just dropped the pk3 in there and it runs fine.
But I would get all of WFA just so you can have it, when 3.99 is released it'll be using the WFA maps anyway, just adding one (welt-wfa).