It depends on what you want. The EQ should only enhance or manipulate the already "good ,quality sound". you can get away without one but it's really up to you and what you want. i currently don't have an EQ but i can filter , boostor cut with my crossover. if i had an EQ it would only be inserted after i got my system sounding good first. Hope this helps.
i would just use my volt meter and see which wire had the 12 volts switch and 12 volts constant then cut those 2. I would wire a different ground to the metal behind the dash. I have a 2003 Dodge ram and the 12 volts wires are the outside wires in the harness. i would think that they wouldn't changed it but verify with a meter. Hope this helps.