How hard is the NASD series 55? Is the STC studyguide good enough?
Depends on your aptitude for the subject. Based on the Series 7, I would say that you need a very strong aptitude for technical terminology and math. The study guide may be good enough, but I would suggest going to the largest library in your city and browsing all of the matierial on the subject, or purchase a comprehensive 55 study guide kit online.
I've read it like twice (I am a convert of 1.5 years)  But my favorite always happens to be D&C!  That I have read a million times.  I love section 132!  Everytime I read it I remember truely how much our heavenly Father loves us!  \n\nJust got married in the Manti Temple 2 weeks ago!