To answer your question on the dual layer movie, yes, many different types of software will tell you the size of the dvd you are attempting to copy. In fact, most commercial dvds are dvd9 (dual layer size), so you should expect to find them that size. This is the whole reason software such as DVDShrink, CloneDVD, DVDRebuilder, etc. came about---so that you could reduce the size of the movie to fit onto a dvd5 (single layer) disk.
And if you are using Windows, just put the movie in the dvd drive, right click on the drive in My Computer, hit Properties and it will tell you the amount of data on the disk. If it is over 4.3Gb, (approximately) you've got a disk that can't be copied straight over to a single layer disk.
If you want to copy the entire movie onto a DL disk, I suggest using DVDDecrypter in ISO Read mode, then burn to your dual layer disk with ImgBurn. If it has an advanced protection scheme that Decrypter can't handle natively, then my favorite way is to use AnyDVD in the background, then use DVDShrink to output to an ISO (without using compression). Then burn with ImgBurn. These techniques will keep the layer break set correctly. Remember to exit AnyDVD before burning with ImgBurn.
There are other combinations that will work just as well though. And I have to admit, I don't often do this method. Most of the time I'll just copy the main movie. If I want to look at the extras, I'll just dig out the original disk.
As to your choices on a burner---I think you've got a very good selection.