What Size Do You Like for Reef Sump in 4x2x2 tank Stand?

[my3kidsdad]

We intend to build a reef with fish, live rock, and coral. Before we start building our first stand we wanted to get the sump size right because it may be difficult to install if there is not enough room in the stand.

Which brought us to the question of what is the best sump size for a 4x2x2 tank? Should we determine what filters we want before we decide what size the sump should be? Hopefully we have these questions in the right order.