I'm not sure I'm entirely getting what you're asking. Are you saying that you want your Applications folder displayed each time you open a Finder window?
You can set that in Finder --> Preferences --> General. There's a drop-down box that lets you select how new Finder windows open.
You might also want to have your Applications folder in the Finder Sidebar (if you don't already...it should be there by default) for easy access from anywhere in the Finder.
Edit: Regarding your other question...DVD+RW supports random read/write, so you can add and remove data without having to erase the whole disc and starting over. In this way, it sort of behaves like a hard drive. DVD-RW does not support this, so you would burn the disc once, and if you wanted to change something on it, you'd have to erase the whole disc and re-burn it with the changes.