Probably better off asking this in the media section - I’m sure a nice mod will move it for you.
Anyways here’s my 2 cents:
Dual layer DVDs are not needed to back up movies. You can usually shrink them down to 4.7GB movies so they fit onto a single layer + or - R. There’s no real benefit of +R over -R. They both work fine, they burn a little differently and aren’t made exactly the same but they both end up working very well at the end of the day.
Verbatim 16x +R is highly recommended in the forums, simply because it does better in “quality scans”. The fact is that the -R 16x is also very good and although it does not score as well in “quality scanning” it does work very well and hardly anyone ever has problems with it. So do not be afraid at all to buy -R verbatim media
With Dual layer VS single layer - dual lyer pretty much has no loss in picture quality since there is no compression required. If you use the right program with the right quality settings, you’ll find that even the single layer compressed backups look almost identical to the original. In my opinion it’s not really worth backing up anything onto Dual Layer unless you absolutely must have zero loss in picture quality.