Hi jokercrow,
Yes you can play Dota 2 on a mac mini.
Dota 2 Minimmum Requirements:
CPU Speed:
Dual core from Intel or AMD at 2.8 GHz
RAM:
4 GB
OS: Windows 7
Video Card: nVidia
GeForce 8600/9600GT, ATI/AMD Radeon HD2600/3600
Free Disk Space: 8 GB
From the
GPU hierarchy chart the 5000 will perform just about equally to the GeForce 8600, while the Iris Pro Graphics will perform quite a bit better. If you're on a budget you could get away with the 5000, if you want to play it with a bit higher quality get the iris.
I'd recommend getting 8GB of RAM, though again 4 would be sufficient if on a tight budget.
An i5 is all you would need for that, an i7 would be wasted in that build.