I believe almost all CNC machines are exclusively windows based? I could be wrong, but I don't know of any cad programs for mac, but I never looked. So I wouldn't worry about the OS. Smaller/larger is better all depends on what you want to do. If you want it to play around and don't have a specific thing in mind, yeah bigger is better because you won't be limited by your machine. If you are dead set on US based Epilog is, from my understanding, the cream of the crop. But others disagree. Honestly if you are mechanically inclined and not afraid to get your hands a little dirty Chinese machines are great for hobby work, and if you invest in a good brand, they can be good for production work too. Support is pretty good on here, lots of people with lots of experience willing to help out a friend.