The light used on Kindles is amazing since the light is projected down toward the screen rather than up in your eyes. Amazon developed this technology and patented it (hopefully it will be sold to computer monitor makers one day), and it's basically equivalent to pointing a light bulb away from you rather than in your eyes. This technology helps reduce eye strain (that burning feeling you may get if you stare at a screen for awhile), but it will still happen.
The Voyage has the same light technology as the paperwhite, however, they have added a sensor to adjust the amount of light projected based on the conditions of light around you. This seems like a gimmick, but so far seems to be a great feature as most people don't change the light often, but when it's automatically done, it helps greatly, and allows for an even greater amount of time before you have eye strain. The Voyage so far seems to be great, although there does appear to be a flaw in some of the screens (uneven yellowing of the page-you'll find lots of info from google), and of course there is a bit of a sticker shock associated with it. Also, if you want a solution immediately, you'll have to wait with the Voyage as there is presently about a month wait if you order it today (11/4/14).
In regards to storage, if you're not putting mp3s on the kindle (something you would only do with the audio version of the kindle), then you should be fine. I have over 600 books on my kindle with about 1/3 of the space left. I notice that autobiography and non-fiction titles tend to take up more than fiction, so you may want to keep that in mind, but storage doesn't seem to be a ceiling that the average user, or even super user, hits.
In regards to your model and dictionary pronunciation, it's not possible. The only way around it is to temporarily turn audio on, have it read that part of the book, then turn it back off. The audio feature of a dictionary is incredibly amazing and important, but for some reason they didn't include that support in the kindle model you have (I had the same model). I keep my phone near me when I read and use the dictionary.com app for pronunciation, hardly ideal, but it works.
As for light alternatives, I personally tried several clip-on book lights (name brands and cheap knock offs) and did not like any of them. They added weight, got in the way, fell off easily, produced uneven light on the screen, and overall just made reading on the kindle clumsy and awkward. I ended up buying a new bedside light as I was never able to find a nice mobile solution (until the voyage!).