I import cad data most days for my job, here's my 2 pence.
Forget about materials. CAD software can assign a colour, maybe apply a basic 2D image, but it doesnt tend to go much beyond that. The materials youll get through into c4d are pretty much going to be a slab of colour; in short you're going to have to remake and apply materials no matter how well your cad data comes in.
What you want from your client is either photos of the product and you do it by eye, a physical sample and you do it by eye, or some sort of CMF document, Colours, Materials, Finishes. It will list stuff like "Black PET plastic, MT10020 textured finish, semi gloss" for each and every part. You can then go through and apply materials as needed. This document will be what they send the factory so they know how to make the product.
File formats, step is the best youll get. it bundles everything into one file and sometimes gives you base colours. It also means you can select the polygon count yourself.
Explore the import settings!, dont just take the defaults and expect nirvana. You can import materials from cad materials, from cad groups, from cad layers, it depends how the cad guy made the project in the first place. You can also define polygon density; some advice there, set angle to somewhere between 30 and 5 degrees, then play with sag, this controls how polys are added across larger curved areas and not just the corners. 20 degrees angle with 0.02 sag can give a good high quality finish without going mad in rounded corners. Increase sag for few polys on large curves, 0.03, 0.04 etc
Work cad cleanup into your time budget. For a hero product (keyboard, mouse, computer case) we will take a day to tidy the object list, get all the pivots and groups ready for animation and to texture the product.