You might find more general commuter bike buying, and bicycle commuting advise in these questions:

• What do you wish someone had told you before your first commute?
• Bicycle for 2 x 30mins commute

My general advise for your specific points would be:

• Rain IMHO means you want fenders, unless you enjoy turning up at work with mud (or worse) all over your face.
• Disc brakes usually mean more expensive bikes and slightly less maintenance. If you can afford them, and you can park your bike somewhere safe both at home and at work then go for it. Otherwise, V-brakes are almost as good wrt stopping power and durability.
• Maintenance wise you might consider an internally geared hub rather than a derailler. Any shifter that will at least allow you to keep your hands on the steering wheel will do.
• A little wider and some threading is enough in most commute situations.

You might find more general commuter bike buying, and bicycle commuting advise in these questions:

• What do you wish someone had told you before your first commute?
• Bicycle for 2 x 30mins commute

My general advise for your specific points would be:

• Rain IMHO means you want fenders, unless you enjoy turning up at work with mud (or worse) all over your face.
• Disc brakes usually mean more expensive bikes and slightly less maintenance. If you can afford them, and you can park your bike somewhere safe both at home and at work then go for it. Otherwise, V-brakes are almost as good wrt stopping power and durability.
• Maintenance wise you might consider an internally geared hub rather than a derailler. Any shifter that will at least allow you to keep your hands on the steering wheel will do.
• A little wider and some threading is enough in most commute situations.