Yeah linking your Wii can be a nightmare - mostly because Club Nintendo has a specific site for each country rather than region. However so long as you're registered on the site you'll be able to trade in stars for Wii points. TBH I'm not sure what the advantage of linking your account is, especially since any Wii points 'bought' on club Nintendo's sites are added to your balance via a redeem code - and the code can be used on any Wii from your country.
Regarding the serial number - you'll find it on the base of your Wii (not the back like other consoles).
Shame they killed off Game Cube stars.
Also be aware that only official Nintendo products have star points with them, not including peripherals.
Keep an eye on the blog for TB Wii info & news.
http://blog.toribash.com/