The bike is fine on the freeway for regular short trips or occasional long ones. It's a high revving motor so as long as you don't worry about the revs a cruising speed of 75 - 80 mph is doable. Your lack of experience is a bigger issue, so get a few short freeway runs for freeway experience, and a couple of non-freeway rides of over an hour before you combine the two.
If you decide to store it for three months there are plenty of threads in the 250 section to search. Basically, for that length of time it doesn't really need anything more than drying out the fuel system, filling the tank and disconnecting the battery. Battery should have a trickle charge once a month when it isn't in use. Oil change before storage is also a good thing to do.