For me it was easier to learn moi than any other modeling program including subdivision modeling thats a way harder than NURBS but if you came from a subD environment it may take you time to get used to it, but believe me, its very very easy!
I also use a Carvewright and Moi is perfect for it...the stl import great if you have stl importer with CW. Just make sure everything is joined in moi or when you import into CW's Designer software sometimes you end up with very small pointy spikes...they wont carve..way too small..but look annoying. Other program I use a lot is zbrush after moi...but you can do a lot of the same things with sculptris and it's free.