I have a new Mini with 8GB of RAM. The 288MB graphics is the minimum, it will automatically increase if it can, mine is 512MB for graphics. On WoW I have all of the object settings at Ultra, but all of the skin settings to fair or low, and I get 26-40fps. I don't know how well other games will run. It also gets hot when playing games. If you are not sure about a memory upgrade, get Apple, or a real technician, to do it.
As for portability, buy an old laptop. If you move it between home and office, then it may be OK, but I don't imagine that people will like you grabbing screens, mice, and keyboards off library computers.
I got you for the portability part. Thanks!