I agree with Simon, the first thing I would try and do is to play a Rick 330/12 or 360/12 to see if you are comfortable with the smaller nut size. For my scratch built 330 copy I'm going with the Rick 660/12 neck dimensions because the nut is quite a bit wider and even though I haven't played a 330 or 360 I know that with large hands I am going to find it difficult. If you are ok with the narrow neck then as Simon has alluded to the most complicated part is the headstock. Also as a side note I'm not familiar with the construction of that kit so I'd want know that the tailpiece was secured into somewhere solid because a 12 string has significantly more string tension than a 6 string as well.