Alienware18 R2 Upgrade question

To answer your questions.

• You probably have the 3-pipe heatsinks (I think they come standard in the m18x / 18), so all you would need for extra is thermal paste and thermal pads, btoht of which are cheap to acquire. Some upgrades do require either a modded vBIOS and modded driver, both of which can be acquired in notebookreview's forum or techinferno's forum (under the Alienware section)
• As for the hardware upgrade process, you swap the MXM GPUs (out the old and in the new and better). 

You said 18 R2, but no such laptop exists. There's the m18xR2 (2012 laptop) and the 18 (2013-2015 laptop). If the latter, the upgrade process is a simple plug-and-play. If for the former, then you'll need a Clevo vBIOS. 

There's also the GTX 970m, which is both cheaper and powerful (more powerful than the GTX 780m and GTX 880m). That would be a good option.

Note: the linked thread is old, before the 18 was recently refreshed with GTX 970m and GTX 980m GPUs.