1) Do NOT buy those motors.
Any motors over 450-500oz should be rated at least 5a-6a for best performance.Look for motors with an Inductance less than 3mH. High inductance motors will run very slowly, and have little power at higher speeds.
Cheap chinese kits are often the worst performing options.
Do not choose motors until you've made you ballscrew or rack and pinion choice. The screw pitch, or R&P gear ratio has a lot to do with motor selection.
2) Do NOT buy a chinese Mach3 controller. Most do not support all of Mach3's functions properly, and they have no support. I don't recommend Mach3 at all, as it's obsolete.
What material are you building the machine with? $2000 is a very low budget for a good 5x5 machine.
Very few CNC Routers are rigid enough for high quality cuts in aluminum. You'll still need to take very light passes. A 12"x12" block will take a long time to machine.