1) Yes, I’m a Ninja 250R owner. I’ve had a 2008 model since late 2007. I also own a track bike (a GSX-R600) and a supermoto bike. While I may sell the Ninja in the next six months or so, it will be for space and money reasons. If I had my choice, I’d keep it forever.
Will you get bored? I don’t know. That has more to do with how concerned you are with learning to ride really well vs. going fast in a straight line. I know lots of people at the track that ride super fast bikes very slowly. That’s a reflection of not really knowing how to ride and not knowing the limits of their bike. So, will you want more power after a year? Probably. Do you NEED more power, and will you have tons and tons of fun on a 250R for many more years? Absolutely. You know yourself better than anybody (I hope), so try to figure out whether you’ll be willing to restrain the urge to accelerate meaninglessly to a super-low speed limit on a bike that’s more expensive, harder to insure, and more difficult to ride.
2) Most people do crash or drop their bikes at some point. I never have (on the road anyway). If you are prudent, patient, and you practice a lot, you can reduce the risk of any such incident dramatically. Drops are always a risk until you know how to manage the weight of the bike, but the lighter and lower your bike is, the less likely you are to drop it. Heavier bikes with higher seats will make it MUCH harder to prevent a tip if the weight of the bike gets away from you. As far as crashing on the street goes, don’t be an idiot. The rest is down to blind luck.
3) You get over this very quickly. A couple of rides and you’ll be fine.
5) It is very hard to stall a bike. You probably won’t ever stall once you’ve learned. In fact, I doubt you’ll stall by the second day of your safety course. Even weenie bikes have much better power-to-weight than cars, so stalling is much less likely.