As far as gaming goes there is just one key thing to remember: games are only going to get more and more demanding so the technical requirements are going to become more and more demanding, even if the game looks, sounds, and plays like a 1990s DOS game.
This has to do with the engines used to program them. "Foxtail" used the Wintermute engine for Chapters 1-3 but now they are switching to a Unity engine. Even the old 2001 Sony, thanks to SwiftShader 2.1 and the fantastic SCUMMVM application, was able to handle the game just as it allows the XP Sony to handle the Vista+ "Znwi Adventure." But with this switch I can almost guarantee this will no longer be the case for "Foxtail" and even the superior 2003 Pentium 4 Dell with its GeForce GO chip won't be able to do it since over at the SCUMMVM site they say Unity is too much of a hassle to deal with.
Therefore anything you get that's "just good enough" for the latest gaming TODAY will very likely be outdated not long from now. Whatever you get, if possible, should be easily upgradable, flexible, and as powerful as you can get within reason. But no "fixed" device is going to last for too long, which is why most laptops are not favored as game devices unless like me you are not into ultra-intense high-specs gaming (even the ASUS is starting to show its age). Spending some more money now for something better could save you hassle and money tomorrow. Decide what you want to do now, what you want in the future, and talk to a number of people into gaming rigs. Their combined advice will best guide you.
In any case, if working on it yourself, get detailed directions and follow them. Those rigs can use a lot of electrical power and carelessness could injure or even kill you. If you are uncertain bring it to a professional or a friend whom knows what he is doing.