1) Wii Play is not the best game, but i did get that deal mostly for the Wiimote. And its $10 extra, thats not too much and Wii Play has about nine minigames which can be quite fun with a mate.
2) Again, i also bought a second Nunchuk my Wiimote and i dont regret it. It doesnt get used very often but if my mates are over we can playing the games which require a second Nunchuk. To answer your question about the Nunchuk there are not many local multiplayer games on the Wii, and the only local one which i can recall on the spot at the moment is boxing in Wii Sports.
3) There isnt a best charging dock since there are many third party ones out there. I would suggest a Nyko charging dock as ive heard that Nyko is a good third party supporter towards the Nintendo Wii.
4) I dont partically see a point in the protective jackets for the Wiimotes, there not much use. But if you must or want to buy one i think there around $10.
5) A charging dock is your best buy at this stage, it will save you the hassel of using batteries.
6) You can purchase a second guitar for around half the price of the bundle package. All you need to do is find a store that sells Guitar Hero 3 for the Wii and see if they sell an extra guitar. I dont think every store does this though.
7) Games i would recommend would be Guitar Hero 3 which seems you are already going to get. Also Legend of Zelda Twilight Princess, Medal of Honour 2 Heroes, Resident Evil 4, Resident Evil Umbrella Chronicles, Metroid Prime 3.
Hope i helped you mate.