I'm not real familiar with your DMR, but it should have some sort of editing function built in. I have a Panasonic unit, but it requires that you have it hooked up to a television set, in order to use most of the functions it is capable of.
You can put anywhere from 2hrs of video to 8hrs of video on a dvd, depending upon how much loss in quality you are willing to endure.. Most recommendations are for 2 to 2 1/2 hrs of video per dvd. If you used compressed formats such as divx or xvid you can get between 3 and 4 and still have decent quality. The best way to find out, is to just try it and see if it is acceptable to you.