You may want to fit fenders and a luggage rack to your bike, this is easier if you get a bike designed for them. You need threaded eyelets on the frame.
Suspension is not something you will need for your kind of riding.
My suggestion would be a bike in the style of Specialized Sirrus. Quite a few forum members ride them and give good feeback. They are light, fast, practical and comfortable. Other brands also make bikes in this style, so pick a shop that gives you good service.
As far as sizing, modern bikes tend to be designed for 1-3" of clearance. The critical dimenison (given adaquate clearance) is the reach to the handlebars so you are not cramped or over streteched. If you are inbetween 2 sizes, then the smaller size is usualy better.