The hardrock is quite OK as a commuter bike, but it really helps to switch to slick tyres. You will go so much faster, and on tarmac they have just as much grip and reliability as knobbly tyres. Some close fitting fenders, like SKS will keep dirty water off you.

Fit a good rack and the toughest pannier bags youy can find. They need to have a quick release system and good stiffening boards. You can go overboard on pockets and zips, I prefer simple ones.

I ride all winter in the dark, and use a blinking rear light (+ reflectors). My front lamp is a standard dynamo lamp wired to a lead acid battery in an old waterbottle, with a constant voltage charger (auto switching from bulk to trickle charge) from an electronics store. It was a fraction of the price of most high power lamps, but has much better battery management than most of them.
Small handlebar mounted rechargeable units or LED ones are not really powerfull or long lasting enough. Hi lamps are a thief magnet, another accessory you have to strip from the bike every time you lock it up.