If you are going to flush mount it, allow a little wiggle room. If it is exact, you won't be able to make the minor adjustments that are sometimes necessary to get a good corner. And if the moulding is off a little, it will drive you crazy. I have mine 1/8 inch about the table, but 1/16 is probably enough. If you shim the underpinner, you can adjust the height it until it is just right. Works with some long and short sticks before doing anything permanent.
I have mine on a stand, with a sheet of plywood mounted to the underpinner.
Similar to the idea of wings, but with the space between filled in.
I'm not sure why this exact shape was used (It is asymmetrical), but I am very used to it.
I bought an extra V-naile, with stand, in the fall at a good price, just in case.
Planning on making a similar top.
I've never had a problem with the nailer being flush.
I did make my infeed tables on my Pistoriouses (Pistorii?) about an 1/8" below the height of the saw, for the same reasoning as your underpinner.
Occasionally it is annoying on larger/heavier moulding pulling down from flush.
Brian