Welcome Jeremy!
Never listen to dealers (applies to both bikes and cars). They generally work on commission so they're always gonna try to sell a more expensive item. Bigger bikes will costs twice as much as a 250 and insurance rates are insanely higher esp since you're new.
Also, learning on a bigger bike is a lot more dangerous. You will want to get your muscle memory down and be smooth with all your movements before moving up. Most people will own more than one bike in their lifetime so just think of it as your learning bike. If you want a little more power, there's the 500r or Suzuki gs500, but both are not eye appealing in my opinion.
Read this thread about top speed/highway.
http://www.ninjette.org/forums/showt...hlight=Highway
I ride on the freeway everyday about 85-95 indicated without issues.
250's are more flickable (turn faster), is lighter, and has great mileage. The only advantage bigger bikes have is better acceleration and higher top speed; both things that a new rider won't be able to use/control wisely. I do prefer my bigger bike on the highway, but my 250 is more than capable of handling it.