I am working on a huge file in Photoshop (CS3) of a map sized 7648 pixels x 6158 pixels at 300 pixels/inch. In metrics it's 65 cm x 52 cm.

The reason why I keep it this large is that I would like a nice high resolution print, when I print it.
I have a few questions about this.

a) Is it at all necessary to keep it at this high resolution to get a nice print?
b) At what resolution does DrawHexGrid produce its hexes?
c) What size of 1 hex do I have to make my grid so 44 fit a 300 ppi map?
d) How many hexes do I have to make per row and per column to make it fit a map like mine (or whatever size except 72 ppi)?

Thanks in advance.