The 18 to 300 DX Nikon lens is fantastic. I bought one last August when they were released in the U.S. and mounted it on my D300.It performed flawlessly on our two week Mediteranian Cruise in September. The stabilization allows hand holding even in lower light conditions without added support. It also allows indoor photography in buildings like churches without flash. The lens is a bit heavy, but compared to the backpack of f2.8 optics I left at home it was a wonderful walkabout lens.
By recomposing they mean if your meter is center weighted you place the center on the subject you want correctly metered, then holding the shutter button down half way you move the position of the subject in the viewfinder to where you want it for best composition then finish pushing down the shutter release to capture the image. You don't walk forward or backward as that would change the metered area and result.
CD's are good for a few years, DVD's last a bit longer. Then it also depends on the quality of the disk you buy. Unfortunately there is no permanent storage method for digital images. You have to keep updating the storage as the media changes. Oh yes- do have a spare "player" for whatever media you store on- the players become obsolete too.
Photoshop Elements 11 does many of the things that Photoshop CS6 for Photographers does, but in automated form. Instead of having to create a layer, make a mask, fill it, reverse it, etc you select the effect and apply it and a pre programmed set of actions takes place to create the result. You have less control than with the full Photoshop, but the learning curve is much more user friendly and it will allow you to do most basic editing and correcting of images. As mentioned, PSE 11 is on sale at Costco for $49, a full version of Photoshop costs hundreds and is much more difficult to learn. Lightroom 4 is basically a storage and cataloging program that also contains simplified versions of some Photoshop editing tools. It can be paired with either Elements or the full Photoshop for a complete system.