[Exmortis]

Some tips:

Screen: Go big! 1080p is great and no less than 13.3' if your not using external screen. I am partial to 15'.

RAM: 4GB is all you need, 8GB if you can find it in budget, as you likely run x64 OS.

CPU: Less cores and more Mhz. Nothing here is multi-threaded, so look for no more than 4 cores and higher Mhz.

Weight: This is not an issue, as it will be less weight then books! But keep your back in mind.

GPU: Frankly any will do here, even Intel crap. Nothing is graphically intensive. However if you also run mapping software, look for 8GB as you will lose RAM to GPU Cache.

Any Intel or AMD CPU is a fine choice, AMD APUs offer better GPU for the money, Intel slightly faster thread to clock (Pre Risen).

Surface Pro is awesome but costly and high res screen is small and HL isn't a great scaling app. ACER is a good mainstream choice, as is Dell, or HP. Asus or MSI are also great choices.

End of day budget is key. My system for PnP gaming is a Surface Pro 3 (i5, 4GB, 128GB) and runs it all but screen is small.