Personally I would have both monitors the same size and model, just to keep it all simple.
But, this then depends on your budget. It may not allow for 2 x quality monitors.
I would also consider 2 x HDD (1st for OS & programs, 2nd for data/images)
If you do go dual montor setup, make sure your graphics card is upto the job.
Get one large card (2GB+) instead of 2 x smaller ones(1GB+), there are still some issues with crossfire/sli.
This might be useful if you end up with different size monitors.
http://windows7support247.blogspot.com. ... ows-7.html
Good luck with the project.