A hub gear cruiser style bike is good for getting around town, but you seem to have larger ambitions, and you will probably find that you are capable of some serious distance riding after a bit of practice. A flat bar, touring style road bike would seem ideal. The Specialized Sirrius model is a fine example, with a quality lightweight frame, plenty of clearance for wide tyres, luggage rack and fender fittings, a sensible set of gear ratios and a good carbon fork.
For sizing, you should ensure a comfortable reach to the bars. Most modern bikes have plenty of standover clearance. A good bike shop will help you pick the right size, but beware trying to offload the size they happen to have, rather then a slightly larger/smaller one. The first step is to pick your bike shop.