Never bothered with fenders or waterproofs. Buy a Buffalo Special 6 shirt - not waterproof, but will keep you warm and dry (ish) down to freezing point if you're generating a bit of heat cycling, even in moderate rain/heavy rain, and they dry out ridiculously fast. Fantastically durable too, mine's 5 years old, very well abused, and still perfect. Not sure if they do pants in the same pile/pertex combo, I'll investigate come autumn.

My main concern is being seen by cagers. Lights, lights, more lights, reflective tape everywhere on the bike/luggage, and a hi-vis mesh jacket. I look like a travelling UFO/Xmas tree... I'll also leave half an hour earlier on the way in and later on the way back if I can just to let the rush-hour traffic thin out a bit.

I'd say slow down a bit, but I'm about 5 minutes faster each way on my daily commute in the rain for some reason. At first I put it down to lower rolling resistance or some such scientific mumbo-jumbo, but really I think it's fear - all that lovely adrenaline!