An EQ is wired pretty similar to an amp. It has a power cable that runs to the positive terminal of your battery, a turn on lead that runs to the head unit, and a ground. As far as RCA cables go, you run a set from your head unit to the EQ, then up to 3 more RCA cables to the amp(s) for front speakers, rear speakers, and sub.
And here's link for the speaker brackets:
6½" Speaker Adapters Nissan 240sx 240 sx 89-94 Front | eBay