I think certainly at the moment your two nunchucks is easily enough, i currently have two remotes and one nunchuck and am considering a second nunchuck (dunno if they are still scarce here in UK)
The only reason to have more than 2 nunchucks is if you will be playing a lot of 3 or 4 player games like red steel, or SSXBlur....so if you are a 4 player shooter fan, or a boarding game fan you might need more than 2.
as for SSB:B, if you check the site (www.smashbros.com) there are 4 ways to play apparently, either using just a remote, a remote and nunchuck, a classic controller, or a GC controller......it doesn't say what buttons do what though yet so i'm not sure what buttons you need when using the remote on its own.
and for the 3 games you have ordered, only the boxing bit of Wii sports needs a nunchuck, so for two player boxing you need two.....and in Wii play you can (but are not required to) use a nunchuck for the tanks game....but after a few weeks Wii play will probably only come out to play once a month (charge, shooting and tanks are good party type games, just a shame they are only two player max)
