As has been mentioned, FZ6 has a 19L tank. My old FZ6 pretty consistently returned 300km until the reserve light came on, or 360km to bone dry. Didn't really matter how I rode, what speed I rode it at, stop/go, highway, 100km/h winds (screw you South Dakota!) didn't matter, it was always around the same mileage. One exception being high altitude, my fuel economy was probably 15-20% better at 10k feet than sea level, but I had zero power.
If I'm on major roads, I'll generally fill up when the light comes on. I've never run out of gas on major highways. If in the boonies and not sure where the next gas station is, I start looking around 200km or even sooner depending on how remote I am. New Mexico taught me that...
CAA Plus is a must, saved my wallet many times, add on CAA medical too. I buy a yearly policy from them so I don't have to get a new policy every time I cross over. They paid for my broken arm in Virginia without much hassle.
Repeated 1000km days are really hard on the body, trust me, I've done lots of them. I generally have zero issues doing singular 1000 plus km days, but start stacking them and you're going to get sore and tired super quick. Whenever I've gone touring for a week, I'll generally do 1000-1200km days for 3-4 days in a row then take a rest day then repeat. That rest day usually consists of me lying in bed unable to move for the whole day. Probably my most condensed trip was 8k km across 8 days of riding, one of those days was a rest day, didn't even want to look at my bike for a week after that. For me, 6-800km is the sweet spot of making ground but not killing my body. There's also a huge difference between straight highway and curvy scenic roads as far as their effect on you and the time it takes to cover ground.
If you want a good warmup to see how your body deals with the long miles you can try a trip to deals gap on a long weekend. I'll generally do this once a year. Day 1, take the interstate south to Robbinsville or thereabouts, it's about 1300km. Day 2, ride Deals Gap and general area, start heading north once you get tired of the twisty roads (I'll generally cover about 400km of highway going north). Day 3, straight home, about 900km of interstate.
Most people will tell you to take breaks often, I'm actually the opposite. I find I tire a lot more if I take a 30-60 minute break here and there versus just hammering through the miles. If I feel my focus on the road wavering, an energy drink is a life saver.
BTW, good looking bike. Makes me miss mine,
http://i.imgur.com/zW9yAfk.jpg