I have 2-way (for now) components in kick panels and subs. If you lived near me I'd let you have a listen and you'd see that there is no need for rear speaks. Even from the back seat it sounds great. Get some components (even in the doors is fine) and a 4 channel amp for now. Bridge the amp down to 2 channels, turn the gains down and save up for a sub. As cool as subs are, you wouldn't be in a hurry to get one if you had a decent front stage powered by an external amp. Get 5.25 or 6.5 components and the midbass would be enough to hold you over.
ps - only use deck power when absolutely necessary!
