Solving the 4x4

Yup, basically when you've solved all the edges + centers, it acts like a 3x3 now...
Now, you can solve it using your favorite 3x3 solution.
If you don't know (I thought you did?), you can check out the one I wrote here.

However, there's one (ok, maybe 2) problem that you might run into (next step)...

(Like a 3x3 solve, I average around 30~40 seconds.)

The 4x4 Edges Problematic Parity
        4x4 Centers.                  Really annoying...