buying new is nice but if you can get a second hand board that you like and rides like you want it get it. my first 2 boards were second hand and there was no problem with them. Last years boards are awesome still riding one today.
yes they did go through stages, in the begining they were BIG then they got shorter and wider and now it seems that they are getting longer again, i meen to get a 125 these days are hard most of the boards begin at 127 and 129 seems to be the most popular.
but once you get the hang of kiting ride a 129 for 5 minutes then get back to share and ride a 125 you wont believe the difference. I come from a skating background and the smaller boards just feels better for me, turns tighter, edges harder, most freestyle boards have less convex to allow for surface rotation and I think the smaller size makes up for this as it edges easier.
So go out and ride them all and you'le know whats right for you...
Hatteras you say...you're so lucky.