1.) When it comes to engine displacement, there is a level of diminishing returns. An 1800cc V-Twin is not (necessarily) twice as powerful as a 900cc V-Twin. However, larger displacement motors will have much more torque and provide that torque early. That means they can run at a much lower RPM on the highway without needing to downshift to go over a hill. That is desirable for those who spend a lot of time on the interstate! Most larger displacement motors are geared much slower (in terms of RPM) than smaller displacement engines. That said, displacement doesn't tell the whole story. The fuel injected Vulcan 900 has nearly the same performance specifications (Same horsepower and only a few ft lbs of torque less) as a Vulcan 1500 engine. Of course on the flip side, the Vulcan 1700 engine is built with the same up-to-date technologies as the 900 engine, and is much bigger (and thus develops much more power)
The other advantage of larger displacement bikes is weight. For a long ride a heavy bike is advantageous as it makes for a smoother ride, and you are affected less in the wind.
The DISADVANTAGES of a large bike is the fact that it'll burn more fuel. VN1700 guys report in the mid 30's to mid 40's. Some 900 owners report that as well, but most of us get into the upper 40's and 50's, sometimes even low 60's! A smaller bike is easier on a beginner, because it's less weight to deal with when you come to a stop (a new rider might have a few times where they stop awkwardly and end up putting the bikes weight all on one leg, I know, I did it several times, which is why I'm glad I started on a 900!) It's also easier to manuever in a parking lot, and easier to throw around corners.
This, by the way, is all a 'general' statement. There are exceptions to every rule. A 2,000cc Vulcan won't touch a 4 cylinder 600cc sportbike. Not in the straight line and definitely not in the twisties. But on a long ride (or perhaps a tractor pull! LOL) the VN2K is gonna win. It's all about how you ride and what you want to accomplish. Remember the more horsepower you squeeze out of a given size engine, the less reliable it's going to be. A sportbike engine is built for pure power. A V-Twin has an element of reliability in the design. An 18-wheeler might only develop 400 horsepower, 800 lbs of torque out of a MASSIVE engine (around 10,000 cc's for several Detroit Diesel models!). But a gasoline engine half that size and much, much less weight could produce that same horsepower and torque with the right aftermarket parts (and lots of 'em). But that ultra souped up 350 isn't going to last a million miles like that 10L diesel will.
2) This is a Vulcan forum, so most of us have experience with the Vulcan. It all depends on what you want to ride. I think the Nomads are a great choice for you. I'm a big guy too, I ride two up, with luggage, and can handle the highway on a 900 Vulcan. It would be nicer on a Nomad though.
Fuel Injected; Here is what you're gonna hear, 'I know how to work on a carb'. That's true, you can work on a carb, not much you can do to an FI system except replace parts. However, you aren't going to HAVE to work on an FI system. Very rarely do issues pop up with the FI systems. Carbs, however, need occasional maintenance and adjustment. The main advantage of fuel injection is this, the injectors make a fine 'mist' of fuel to spray into the engine. The carb will do this too, but not quite as well, and not until it's warmed up (that's why a carbed engine needs a choke and runs rough when cold). That means with fuel injection, it doesn't matter how cold it is you just hit the button and go. Throttle response is also smoother and, generally speaker, a fuel injected bike will make a little more power than it's carbed counterpart.
Air or Water; The proponents of air will say water cooling is one more thing to fail or mess with. That's true. Due to the small size of the cooling system the coolant must be flushed every couple of years, things can leak and fail and leave you stranded, etc. But I personally prefer liquid cooled. You will still have some heat, but not near what you'll have on your legs with an air cooled engine in the summer. Liquid cooled engines tend to last longer as well, as heat is a major destroyer of components, and the air cooled engine will run hot more often than a water cooled engine. Not hot enough to make it seize or anything, but hot enough to accelerate wear.
Chain/Belt/Shaft. I don't like chain. The main reason is, the chain and sprockets need to be replaced ever now and then (20k miles seems average), they need to be oiled and cleaned, etc. It's a lot of maintenance. I ride a lot, and I don't want to put up with that. A belt drive will transfer as much power as a chain with no maintenance, however, it can break and be very expensive to replace. This is rare, but it does happen. You'll want to use caution on gravel roads. Shafts are the most reliable if properly maintained, and will probably last the life of the bike without any repair or adjustment (just the occasional grease and lube). But it robs some of the horsepower from the engine. My wife rides a 750 honda that is shaft drive. Smooth as butter and pulls my big butt on the highway at 75 (when I rode it home from the dealer), so I'm sure a larger bike with a shaft drive wouldn't be an issue.
4) Just figure out what YOU want out of a motorcycle. People will tell you what THEY want out of a motorcycle, but THEY are not YOU. If what YOU want is to take long trips, travel, commute, or make your motorcycle your primary mode of transportation when the weather allows; get a bike with a big motor, good solid brakes, and plenty of storage. (Nomad would fit here great, or a Voyager!). If you want something that gets better gas mileage and can be thrown around in the corners, fast, etc. Then a sportbike might be for you! If you are wanting sleek looks, an occasional around towner, etc. Then a 'classic' model Vulcan (they've got 'em all the way from the 900 to the 2000!), or the VN900 Custom is the way to go.
FWIW, I ride a VN900 Classic LT. That's because it was my very first bike. I am elated with this decision 20,000 miles later. The reason is, now I have some miles and can confidently handle a larger bike. But I'm in no hurry to trade up. The 900 does most things well. One day, I'll trade it in for a Vulcan Nomad, H-D Road King, Honda Goldwing... something along those lines, something built for the long haul and touring (because that's what I love to do). So if you are like me, and love to tour and spend a lot of time on your bike, but have a little more experience than I did when I was shopping (and it sounds like you do!), then I would really encourage you to look at a touring model bike.
Here's my checklist for a touring bike;
1) Dual Disc brakes up front. Good strong brakes are a must for loading the thing down.
2) Larger displacement engine that is geared to run low. Don't worry about how many gears it has. My buddies Ninja runs at 6,000 RPM's on the highway in 6th gear. Find out what RPM it runs in top gear and look for a bike that lumbers along, whether it's 5th or 6th.
3) Dual shock rear suspension. A mono shock is adequate, but a dual shock suspension will be much nicer. Adjustable rebound and air shocks are a plus too.
4) Wind protection. Fairing/windshield/etc. You'll definitely want it on a long trip.
5) Storage. Hard, waterproof, lockable storage is a must for a long trip. Though, these can be added later very easily (as I did on my 900!)
6) Large fuel tank. You want something that can handle 200+ miles on a tank of fuel.
"8 But God demonstrates his own love for us in this: While we were still sinners, Christ died for us."
Romans 5:8 (NIV)
2014 Kawasaki Vulcan 1700 Vaquero ABS SE
iPod Connector Kit, Kuryakyn Highway Pegs, Mustang Touring Seat, Marvella's Hitch, Kuryakyn Trailer Wiring Kit, Haul-Master Tag-a-Long Cargo Trailer
2011 Honda Shadow Aero 750 (Wife's)
Memphis shades quick-release windshield, OEM Solo Seat, Mustang Fender Bib, Chrome Solo Luggage Rack
Past: 2006 Vulcan 900 Classic LT