An '05 VN750 is an excellent
step up from the 250.
I also bought a used '05 model, with a little less than 1,600 miles on the odo.
This '05 bike is really too new, with too few miles, to have much wrong with it yet.
If the bike passes a good visual inspection (no evidence of a drop or spill--be sure to also look at the sides and underneath the pipes for scratches!), then.....
I recommend asking the dealership to do a driveshaft spline inspection, and swap out the battery for a maintenance-free (sealed) one, as part of the deal with you. Explain that the splines have chronically left the factory on late model 750's with little or no lube on them.
Check the battery holder box (and beneath it) for evidence of a battery fluid leak--you'll see corrosion damage (no paint) or evidence of a white/chalky powder. Also, look for corrosion damage on wiring/electricals underneath the battery (e.g., the regulator/rectifier area). This is merely a check for a faulty original battery.
If the splines are found to be dry (or nearly so), have them lubed with a "moly 60" or better compound (like Honda moly), and not
just any general purpose grease.
Another good idea is to do a stator/electrical system check (for proper voltage amounts at various rpm's).
There's more info here on this forum for how to do all of the above. Just look around.
And yes, take the bike for a good spin--or have a trusted friend/relative do it, who knows bikes.
This bike has some really handy features on it that are no longer found on most other cruisers. It offers a lot for the money, and is really the last of its kind--for now, anyway.
Good luck with the new ride!!!............