If you do a bit of reading on this forum, it should answer a lot of your questions.
However as a quick summary, you can use DL media if you want - personally I don’t use it, still too expensive and variable in quality. I use single layer media and AnyDVD and CloneDVD2 to backup my movies. This software will allow you to remove all the extra’s and then compress the movie to fit on a single layer disc. Or if you want, you can split the movie over 2 single layer discs.
If you do a bit of research you will discover there are free tools you can use as well, and other software you can buy. They all have different plus and minus points, and it will boil down to what you like using yourself.
I would suggest spending a bit of time on this site reading before you make any purschase.