With this headunit is the 5v regulator required? Also can I use the stock amps for the speakers and an after market amp for a sub?

 

Not sure about the 5V....your car came with a stock amp?? If youre going to buy a new HU might as well compliment it with aftermarket speakers that will sound a lot better. I think Infiniti's are less than a hundred now a days and they will blow away any stock speaker without an amp.