I can only make an educated guess here, but it would seem that your aftermarket rims have a larger diameter bore than stock rims. That is the reason for needing the hub centric rings. So, you would need them on the front and back. Depending on the offset of the wheels, this will dictate whether you need spacers on just the back, or the front also. The rings will align the wheels on the hub. The spacers will do 2 things, provide clearance from mechanical parts and/or give you the physical appearance that you desire. So, the short answer is that it sounds like you need the 4 hub centric rings, and the rear spacers.

Question..... Are you happy with the stance/profile with the way the wheels look now? In other words, when you look at the car from a side profile, do the front or back wheels look like they are inset into the fender wells too far?

Here are a couple pics to illustrate this: Sorry for the crappy quality of the pics

No spacers:


10MM spacers on front and 15MM spacers on back. No rings required as they are stock rims.


Notice how the spacers allow the wheels to provide a more streamlined look from the side profile? I hope this makes sense. I know it can be a bit confusing.