honestly, if you can justify spending 350 on a console, then 60 dollars on games go with an Xbox360. sounds like it will fit your son's gaming needs a lot better than a Wii will. but if you like the idea of the 250 price tag (us) than there are 2 tony hawk games available.
to answer your question about the Wii Remote, the nunchuch is an attachment that plugs into the remote, making it one complete controller, but for mini games like wii sports its not required, for full length games, 90% of the time you need the nunchuck.
there's a new star wars game coming otu for Wii (probably early next year) other than that i dont think theres a lego game on the Wii.
the console is very kid friendly and im you could deffinately have fun with it too. theres a few WWII shooters out and the new Medal of Honor is comint out in november so watch for that one (online, 32 players)
as far as war games for a five year old go stay away from call of duty 3, the "motion controls" on some of the parts (claymores, mortor controls) are gimicky and i had trouble with them for a while, they just ticked me off and im seventeen lol.
medal of honor: vanguard wasnt too violent though, he might like that. easy enough to control and play through.
umm thats about it, if u need anymore help just ask.