I'd get more RAM, if possible. And don't bother with a Quadro. AE uses OpenGL so little, it's simply not worth throwing a lot of money out of the window. Most normal GeForce or Radeon cards will work sufficiently.
But I am thinking that I will be using the computer primary for After Effect and Cinema 4D, so I was hoping that the card could support both programs.
Regarding the RAM, I would like 24GB
...I was hoping that the card could support both programs.
Sorry to dash your hopes, but your intended card will NOT help AE. No fancy card will.
You would only be getting this card for its ability to work in C4D, so you might as well do the necessary research to get a card that will work well with C4D.