Hey I have to thank you I only found out about sketchup a few days ago because of this thread. Already have it pretty much figured out check out my design on my newest thread (First 8 str build! Lots of pictures!!).
Anyways design wise I really like your ideas. However I would make the headstock larger because it looks really small compared to the body. Also its a good idea to have the bass strings as close to the nut (within reason) as you can and the treble strings a little further out. The reason for this is because the more length of string there is beyond the scale length the more the string can bend. With that in mind most people seek to have a tight feeling bass side and a bendable treble side. Clearly this can only be done perfectly on an inline but still good for 2+4 or whatever. Either way its a 6 string so I don't think its a big deal either way but just a little info to throw at you. Oh and body wise its really good love the large lower horn.. assuming its out of the way.
Anyways looks good I'll be following this! Oh and check my design out would like your opinion too