1. at the moment, you really don't need to buy any extra sd cards unless you plan on stuffing your wii with vc games. dunno if they're planning on releasing an exterior hard drive just yet.
2. you can go online using a wireless router or an ethernet cable. and no, lag is not an issue.
3. the wii's online capabaility is free of charge! all you need is a working (hopefully fast and reliable) internet connection.
4. idk, my bff jill?