Hi,
how many DVDs you take depends on their usage.
For your archive I would agree to use 4 DVDs but you said this decision will have influence on your further creations.
So let me tell you I also shot about 4.5 hours of film but this was an interactive movie I wanted to share with others. So here came another constraint to use very few DVDs for a better distribution. In the end I was able to put the film on 1 DVD(DL). To improve quality I used only half of the horizontal resolution which causes a slight blur on tv but reduces the artifacts of DVD compression because you have less picture to compress. I used 3500kbit/s and it was quite tolarable.