Back in the old days I did a five day tour of New England on a Yamaha RD400. In comparison, your 750 is a luxury cruiser. More recently, I've done several-day tours on a Moto Guzzi Nevada 750, which is very similar to your bike.
I bought the Guzzi in the picture new in 2006, and my friend (also in the picture) bought it from me last year:
On this trip last August we did a 2000-mile tour through Slovenia, Austria, Germany, and Switzerland. With the Guzzi and my XR1200 a 400-mile day is about as much as we would want to do. The seats get hard, and you get stiff all over. One thing that helps a lot is a bit of sheepskin on the seat. I also found that padded bicycle shorts (under riding pants) also help.
I see in the picture that your Honda has saddlebags. I've found that a top box is even more useful. You can get more stuff in one, and it's easier to get at. I can't make out from your avatar whether your bike has a windshield or not, but even a small one make a big difference on the highway.
We both wore hi-viz vests and slapped some reflective tape on the back of our top boxes:
On a long ride you tend to get a bit tired, so we pull off the road every hour or so for a coffee and a rest. I assume car drivers are tired and inattentive on the highway too, so I always like to keep plenty of distance between myself and everything else on the road.
Got to watch out for traffic jams too:
