Hey Gianluca,
Well, I am not really a specialist on it, I mean I have someone to consult with, but I guess I can give you an idea if I share with you what PCs we use at the moment:
Now, I think you will do fine with i5 and 8GB, and you do not need a special video card.
I remember for MT the most important is the RAM, so if you can afford more is better.