I hope a few others can add to the following.
1. I don't think any yacht has a manual. Plumbing and wiring would have changed anyway.
2. If you don't understand the wiring system, you need to find a competent electrician to help you. One battery is probably used exclusively to start the engine, and a second battery bank is used for house power, including lights. How the wiring is accomplished, however, is probably unique to that boat, as it is to most others. Same with the plumbing.
3. The anode (zinc) for the shaft will be appropriate if it has the same internal diameter and the shaft's diameter.
4. I wouldn't go up the mast while it's on the hard. That is going to place much to much stress on the hull at the contact points where it is in the cradle.
5. The keel should be the primary support point. the boat should rest on the keel and all other supports should be primarily to steady the boat. The keel is usually placed on a large piece (or pieces) of wood, perhaps 12" by 12". Although not a really good photo of Watermelon on the hard, this should help: http://www.fototime.com/A0518F87B6EABF6/standard.jpg
6. Chainplate bolts - if I were you I'd wait for the owners to return to supervise this.
7. I don't know anything about the roller furling mechanism, don't want to try to guess.