I've actually used both applications, a lot. I'm using Civil 3D at about 100% right now. If you were able to get pretty good with Carlson, Civil 3d shouldn't be an issue to pick up, and it's a lot more enjoyable to work with.
one of the first steps would be to find a good template. keep in mind that unlike Carlson, the Civil 3D objects cant be modified the same way Carlson CAD parts could be modified. meaning if you didnt like the way Carlson plotted a profile, you could just manually edit, whereas Civil 3D essentially builds dynamic blocks edited through styles.
The part catalogs are a similar case... the catalog is about the only external file outside of the .dwg with C3D, and you'll want to set it up so that you have some good parts to build from.
As a firm, you also want to determine how extensive you want to model your design. Civil 3D can do a lot, but it doesnt mean it's required... like do you model just storm manholes, or model the inlet up top as well?
Feel free to ask any specific, i can try and translate Carlson - Civil 3D
