In fact, do you have a favorite monitor? In the past I've used 2 monitors, but right now I'm using 1 fairly large one. At one time I used a HUGE one, but found that wasn't that helpful and took up too much space.
I'm a big multiple monitor fan--at least two, preferably three (because I do some typing from copy). It's much more efficient to have your references, including your browser for searches, always displayed to one side as you work instead of having to flip windows back and forth (I'm a big fan of digital references, too). As for the monitor itself--I absolutively, posolutely have to have a rotating monitor that can be put in portrait (rather than the usual landscape) mode. Being able to see your document displayed as the entire 8-1/2 x 11-inch page in true size makes a world of difference. You won't realize how much time you waste scrolling every day until you don't have to.

I'd go for a big landscape monitor only if it were big enough to display two full-sized 8-1/2 x 11 pages side by side. Nothing that big is remotely affordable at the moment.
I agree with changing lighting and positioning to remove any reflected glare, and one of the very first things I do on any new computer is go into display properties and change the background for all windows to a very pale gray-green in my color scheme, which changes document background in Word to that color as well. You need to create a custom color for that, but it only takes a second to do. I find good ol' Eye-Ease steno pad green is much more restful to the eyes than the classic WP white on blue, let alone the glaring Word black on white.