I started my first season of riding on a 2010 Ninja 250R, and rode quite a bit on highways going to/from Port Hope, or other areas well outside Toronto. It's an excellent bike to learn on, I feel I probably am a better rider for having started on it. Had a lot of fun with that bike, despite since realizing it was physically pretty small for me. I realized after upgrading to a 650R and now my V-Strom, that I dwarved the 250R and it showed.
To answer some of the points, in my opinion:
I rarely found much about the bike to be scary, unless I was riding like an ******. (Had a few close calls, nearly got bucked off the bike taking a turn incorrectly.) The 250's very forgiving and generally will put up with either a relaxed or aggressive riding style. I would say to an *extent* there are some risks riding a 250cc-or-lower bike, as you don't have the acceleration power the larger displacement bikes have if you ever need to get out of a bad situation. (i.e. I had a truck veering toward me on a wet highway, and the 250R had a hard time getting up to speed to pass it, that was a bit scary. But as Brian P & others have said, drop down to 5th gear and you'll get the power needed -- I just didn't know that at the time.)
Can't speak for 125cc's, other than from knowing a few fellow riders who had them. But if there's one thing I'd mention about 125/250cc bikes, it's that IF you choose to ride with groups of larger bikes, you may struggle to keep up if they don't consider waiting for you.
