Get the 4 ohm sub if you aren't driving it with a custom sub amp.
Its the same sub really, just 4 ohm vs 2 ohm.
This setup basically deletes the rear speakers in the car. You will not miss them.
4 channels on the amp. 2 channels to the front components, 2 channels to the sub.
You can always add a dedicated sub amp later and then add some small rear speakers for fill.
The factory rear speaker are about an inch in diameter. They are truly a joke, and yours are probably dry rotted by now.
2001 Alpine / Schwartz Coupe
2001 Estoril / Estoril Coupe
2001 Steel Grey / Estoril Coupe
1999 Estoril / Estoril Coupe
Sunroofs are for girls.