I would agree with Liberty's answer above about the factory VN750 seat.
You may find that (with the factory seat) you need to stop every 50-60 miles to give you tush a rest.
But the real
answer to your questioning lies in how the previous owner(s) treated the bike in question. If they've neglected her, she may indeed later give you problems--regardless of how well the bike may have been made otherwise.
Having owned my '05 since almost new, with just one previous owner who simply broke the bike in for me, I can tell you she's been a reliable machine. But I've treated her pretty good, too.
This VN750 forum will nonetheless be very handy for you, as it will educate you on the bike big-time and how to avoid problems with it.
Except for the uncomfy factory seat, the bike has a fuel tank that's a bit on the smallish side for long trips. A tankful will take you about 150 miles on average b4 you need to fill up. There are places out west where another on-board fuel supply will come in very handy. East of the Mississippi River, however, you should be ok without this extra fuel.
Past that, given good maintenance, the bike is actually a very good touring machine. You'll pick up some handy features with this bike that most cruisers don't have anymore.....like a centerstand, a tach, a fuel gauge, self-adjusting valves, and more. It also has tubeless tires, so a flat tire is usually fairly easy to repair away from civilization.
This bike was manufactured with very few changes for a long time (20 years), so spare parts for it should be available for quite a while.
For a cruiser, it has very good power, is very smooth, handles very well, and is fun to ride. With its Ninja-based engine, it is more of a "sport cruiser"...whereas many other cruisers are merely Harley wannabe's.
Amazingly, the bike has very little support from most accessory vendors, despite its 20-year production run. However, some creativity on your part along with help from this forum will get you around this problem in most cases.
The bike will carry a back-seat rider, but it's best if he/she is a child or a small adult. Past that, it's really a solo rider machine.
Hope all this helps with your decision...