I would put eheim effimech in the first layer followed by two layers of either ceramic rings or a media such as eheim pro or equivalent. In a word, bio.
People dont run carbon basically because it is quickly exhausted and vurtually useless in a relatively short time. After carbon has absorbed all it will, it can actually release back into the tank just what it was used to remove. Plus, it isnt exactly cheap unless you get it bulk and then the quality comes into question.
Use carbon to remove medication in the water and then remove the carbon...a properly functioning biofilter will most likely meet all your needs.
I'm not familiar with the rena filter personally but I have heard they are very reliable and a good bang for the buck.