As has been mentioned above, it depends on what your service is and who your clients are. Since you live in the PNW, I suspect that most people you deal with won't be as picky about your appearance as they might be in other areas, as long as you provide competent, timely service; some might even approve of your car-free status. As for clothes and gear: Get GoreTex pants and jacket, and some waterproof shoes. (Don't use sailing-type foul weather gear on the bike ever, they'll turn into a moving sauna.) Waterproof panniers are a very good idea, too. If you have to carry a lot, get a trailer and those waterproof sea bags. Fenders are a must.

Good luck with your business, whatever it is.