I wouldn't have much hesitation in buying this computer, but dell says it isn't possible to swap out graphics cards in this model. Possibly a newby question: Are external graphics cards a thing?
Mostly in more expensive models, and they're not always swappable anyway. That's how laptops are, they're not as modular as PCs. Although Razer got this little thing: Razer Blade Stealth Ultrabook and Razer Core External Graphics Dock
There's lots of variables to consider if you're planning on getting a laptop. It's not as simple as an i5 being better an an i3, etc. For example, you could be getting an ultra low voltage processor, a mobile processor or a HQ one. Each with their benefits. Ultra low voltage for power efficiency but low performance, HQ higher performance but takes more juice, you get the picture. Laptops will also never perform as well as a desktop if it's using mobile parts, e.g. a 980m is beaten by the full GTX 980 graphics card. A lot of people also don't consider the GPU when purchasing a laptop; it's the most important component for gaming. Integrated graphics are just not OK, I'd say at LEAST a nvidia 960m these days. Never buy a macbook. This laptop gives double the performance of the top macbook pro for less than half the price: Inspiron 15 7559 Laptops | Dell UK
You should buy a laptop which is easy to carry, has long battery life and can survive a lot of punishment. After all, you will be using it for studies and not, let's say, to play COD black ops on highest settings? Think one of those foldable laptop/tablet might be the very thing you need.