I am building one also, look at this site
http://www.renderwurx.com/rc/sig4star/
cool looking one, I am going to sheet the turtle deck also, but porbably not go into the balsa cowl looks cool though.
While building add ply to the fusalage starting from the 2" of the rear of the wing, my fellow members told me that he had borken his from that place 5-6 times, till he added ply.
also I am going for a tail wheel assembly to keep my rudder free.
what engine are you puting in?, I have a 46FX going in.