Just some general observations for you. I'm new and finding this out as well, so I might have found something out you should know.
YouTube - IPM Presents: A Beginner's Guide to Motorcycles
1: Seating position; There are a few, but just to cover the basics, cruisers, nakeds and sport tourers have the most comfortable seating arrangement. HOWEVER, IF, you are the type that can handle the discomfort, then the reward you get once at your destination and the type of riding you find there will be a small inconvenience. I.e: you want to shoot some twisties once you get TO, where it is your going, and any other type of bike can't reward you with the same effect.
2: Wind protection; If you're gonna be seeing a lot of highway, you're gonna want some type of protection. Nakeds and sport bikes aren't often the best, but if you're the type that can handle it, then

I put sport bikes into this only because hunched over for long periods of time, most people don't like that... If you can, then good for you. I prefer sporty handling, so I'll choose minor discomfort over a weighty sport tourer or an ill performing cruiser.
3: Tires; If you're wanting to do some mileage, "tires" aren't exactly a minor deal with motorcycles. Most people carry what they think they're going to be using and you can either carry some spares, of pick a good tire to start with and hope you can fix it in the event you need to. Also, tube tires cannot be plugged and the tubes are said to be able to blow at any time. Tube-less tires can be plugged, so they are relatively maintenance free. Weight is a BIG issue for my little 250, so I'll just tell you what I've found out researching tires. Kenda has 6ply tires, are relatively cheap and come with a great web reputation and I've just found out they are...
read here. Other than them, any other china tire will not ever be considered by me...but that's just me.
4: Cargo: You'll need a bike that can handle whatever cargo you decide to use for your trips.
5: Hills, mountains and passing power (that, sadly I do not have

); Depending on what you want it to do, I'd pick a bike that could handle the terrain.
6: Maintenance; There are some shaft driven bikes. This will save you chain stretch and possibly breaking a chain. Other than changing the oil, 2MK, there is NO maintenance on a shaft driven bike.
7: Air or water cooled; Both, IMO, have their upsides as well as downsides, but the air usually looses over liquid (I'll add some later)
just some FFT...