I run 4 T162C RF coaxials in all the doors (i run coaxials cause im cheap), it runs off a T3002amp. I also have a T1 sub, and it runs off a T5002 amp. Do i need a equalizer. I dont know, because i dont know how it works.
I like the function of the EQ sub you could ajust the sub volume and the mid's and high's. If i were you i would buy one.
Depends on u actually.. if u can live without one its okay. Also depends on ur HU, most good HUs have built-in EQs to provide u with some control over ur music. I've got an Alpine 9831 with a builtin Parametric EQ and i find that enough. But a separate EQ can give u easy and instant access to control ur music. BTW, simply put.EQs change ur music by cutting or boosting certain frequencies.