the ipac2 has 28 inputs. you can hook up however many joysticks you want, whatever way you want to, as long as you dont require more than 28 inputs.
most people who have a dedicated 4-way, have it wired in parallel with the player 1 8-way. this is accomplished by either daisy chaning the end connectors or running two wires to the terminal strip on the ipac.
my personal opinion is to forego the dedicated 4-way. you can get a t-stick plus when you get the ipac and have 4 to 8 way switchability without having to open up your cp. the omnistick prodigy is also a good option to consider. most people who come into this hobby always try to cram everything into a huge frankenpanel. in my opinion, a simpler, less cluttered panel would be much better.