My ears get cold when I cycle (50 miles a week, some commute, some leisure) - I have a fleece band that goes under my helmet.
Cycle defensively - if the road is narrow, I cycle far enough out that car drivers are forced to overtake properly. If on a roundabout, I cycle where a car would drive (right hand lane if turning right). I've cycled almost daily for 20 years, and other than one car door opened onto me, never had a collision with a car.
I don't like waterproof trousers (I sweat!) so change when I get to work if it's wet.
If you're in a city, I'm guessing the whole route has street lights. If part of it is unlit, you need a really really good front light that doesn't flash. Whether or not your lights flash is up to you; they do want to be bright.
If you aren't confident about doing your own bike maintenance, you might want to get your bike serviced. Otherwise, if the gears don't quite work that's OK, but the brakes really need to! If, when you pull the brakes on hard, the brake lever touches the handlebar, it needs adjusting.
I'm another pannier fan, but that's personal choice.
Happy cycling!