1 Look at this review over at Anandtech:http://www.anandtech.com/show/3773/amd-and-intel-mobile-rematch-gateway-nv5933u-vs-acer-5542
Looks like AMD will have some CPU's that will be more competitive in the near future. I'd go with core i3 right now, but AMD is cheaper.
2 Depends, for gaming definitely go with discrete. Discrete graphics will obviously cost you more. For photo editing I'm not sure you would see a difference, but I believe discrete would drive a large display better.
3 not necesarily but it depends what inputs your big screen has. Don't know of too many that come with dvi or vga...