I'd suggest giving some thought to the nature of the work you'll be doing on the table before deciding on the table size and location of the mounting plate. You'll want good support for the size of work pieces you'll be most frequently dealing with, and on both infeed and outfeed sides. And, you'll want enough table to the back side of the plate to accommodate the fence guides. Although a lot of work positions the bit in, or near the fence, there are operations (dadoes, for example) where the bit is well in front of the fence.
So, while a larger table is more versatile (to a point), the bit-to-front edge distance should allow you to reach the fence line without stretching or straining too much. That aspect, along with whether the router table will also be used as a table-saw outfeed surface, should govern the height of the table surface.