Yet another "which-type-of-DVD-should-I-buy" question

I just bought a VCR/DVD recorder, with which I plan to dub some of my old video tapes onto DVDs. I’d then like to load some of these files onto my Mac and edit them in iMovie, then download the new files back onto the DVD, to play in the DVD player.

So what type of DVD should I be using, and what file formats should I be working with?