Can audio only sources be transfered to DVD with a home DVD recorder? If so, What precautions must be taken?

Yes, you can but only if your sources have a LINE LEVEL output.It means a "fixed" level of around 3 volts, commonly, so you don't overdrive the audio circuits in your DVD. If your source has a volume control, take special care with it. Start at very low volume settings. It works better if you are able to monitor your recording in real time. This way you should "recognize" what the usual volume level is so you don't overdrive it. Digital recorder are prone to distortion once you surpass their factory set levels.

Yes. Line impedance should be the same. That means don't plug a mic into the line input. Remember bad audio in will be bad audio out.