1. The big problem with dubbing sound over domestic camcorder footage is sync drift. Starts out in sync, then drfits out over the length of a shot. At shot lengths over 3.00 mins or so this can become really noticable, especially if you are using a basic editing package like movie maker. If its a singer/singers in close up it will become noticable in much less than that. You will find it might work on YouTube, but it won't work on a TV.
2. You can do mic into radio mic transmiter to radio mic receiver, then to mic input into camera. However, radio muics that work are pretty pricey, and very prone to interferance from other radio sources.
3. It is possible to take sound via cable from desk to mike input, but you would need to reduce the line level output to mic level i.e. attenuate it. You can cobble together something to do this using easily avaiable parts and a soldering iron.
4. Camera mics, even zoom ones, don't work very well UNLESS YOU GET THE MIC CLOSE TO THE SOUND.- inverse square law.
5. Camcorders are sold on the basis of picture quality, not sound quality, you therefore have to work a lot harder to get decent sound
6. The minimum you should look for is a mic input and headphone output. Spend less on the camera if you have to and a bit more on a mic and a decent cable. The only way you will get decent sound is if you get the mic close to what you are recording and in the right place. Sound isn't like light. You can't 'aim' a mic like you can a camera to avoid distracting sound. This isn't so noticable on items that are recorderd in quiet rooms with no other noise to ditsract, but will become very noticable indeed as soon as conditions worsen.
7. Choice of mic is, for these reasons, as important as important as choice of camera. But always remember that a cheap mic that you can get close to the sound source will alwys outperform an expensive mic further away.
8. Might be worth buying an older modelrecording on mini-dv tape, te sound circuit would be the same, but would record on older format.