Are you wanting to playback on a standalone TV dvd player or is playback on your computer fine with you?
The DVDRW, you have to check that your DVD player you are using can playback DVDRW's. If your DVD player can play it, you can certainly use DVDRW's. I'd probably have one DVDRW on hand anyway to burn to. Then if it work fine for you, you can copy to a DVDR, the write once, and once finished, never to be erased DVD media.
As I see it, you usually don't 'add stuff several times the same DVD', you usually just add on one go and burn away. Unless you do something like you don't have a DVDR disc finalized after burn so that you can have the ability to add more content later.
If you are authoring a video DVD, usually you just add all the clips you want to your DVD (assuming all the content will fit on the DVD) and just burn away so you get a video DVD like those you can buy from the store. Usually DVD burning tool will give you indication of whether or not your contents will fit all on one DVD and the quality of the videos burned to it if it won't fit but you 'force' them to fit on.
Or if you want, you can take the videos files (mp4, avi, whatever) and just burn that to DVD (no DVD video authoring) and just playback the DVD on your computer. (Some DVD player can playback DIVX AVI format files burned to DVD though).
Hopefully that helps,
Good Luck