So far the joystick is working fine, I will order one of these adaptor and try it on the pc too

Now that I know how to make one, I will try with a MarkII, with 6 or 8 buttons probably, so it will be totally compatible also with games like Street Fighter.
Also for the case, I will try to make one from scratch; I've used one of the electronic project box, found in an electronic component store; or go for the acrylic custom made case (which is easier, there is a store that makes them right down the street).
I have found a design for an Xbox controller, but it involves removing the main board of the controller. At this point I will be hunting for a broken arcade joystick, which works with PS3/PC and Xbox; in this way I will just use the circuit board (will be interesting to find out the connections thou).
Altho from what I understand, the Amiga support only 2 buttons (and not all games support it), so the other 4 basically will just be unused.