Welcome! I will try to answer your questions in random order. Have you taken the msf course yet?
Clipons are handlebars that "clipon" to your forks, usually below the triple tree. This will push your handlebars further forward and lower.
Not the best angle, but the handlebars in front are my woodcraft clipons I was installing. Once you install clipons, you reveal the top of your forks.
The silver cylinder at the top is one of my forks. You can adjust the fork a little which will reveal more of the top and essentially drop the front of your bike. So yes, you can lower the front.
You will want to learn how to countersteer, not lean (countersteering creates the lean). Once you're up to speed (about 10-15mph), pushing on the handlebars will turn you in that direction; ie pushing the right handlebar will cause you to go right. Just leaning will only move you minimally, you want to control your steering with the handlebars. Your legs won't steer you much at all (pushing down on the pegs is also a whole other story).
Your bike's wheels gyroscope is what keeps you upright and straight on the highway. Pushing your handlebars left/right is what cause you to lean, but your bike will want to go back upright. People one hand on the freeway because it is more comfortable when you have really low handlebars (which supersports do). There's really no need to one hand a 250 since the stance is pretty upright. Wind may blow you around so you will want to stay loose and relaxed. When you tense up, you will usually "deathgrip" the bars which adds extra unnecessary inputs to the steering. The bike and you will be around 500-600 lbs so you won't be blown lanes over, just maybe a few feet depending how strong the wind may be.