For your first question, if you are trying to get a hurdler to stop “floating” over the hurdle at hurdle clearance the last thing you want to do is get them closer to the hurdle. On the contrary, you actually want them to takeoff further away from the hurdle because this will flatten out their flight parabola. If you flatten out a hurdler’s flight parabola their hurdle clearance (the amount by which they clear the hurdle) will be lower so they won’t be “skying” over the hurdle. “Skying” over the hurdle when combined with a takeoff point that is too close to the hurdle is what typically gives the impression of “floating” because it is caused by a sudden decrease in horizontal velocity and a sudden increase in vertical velocity at takeoff. As a result, it looks like the athlete isn’t really moving forward (because of the aforementioned decrease in horizontal velocity) and they are just floating in the air. I think the best remedy for this is to run hurdles at closer-than-competition spacing during practice and gradually increase the spacing to the point they are near normal spacing. This will help with the rhythm of the event. Also, it might help to put something out in front of each hurdle at the point where you should be taking off at…..somewhere in the neighborhood of 2.8-3.1m for a high hurdler.
Acceleration development work away from the hurdles (20-40m sprints) is good for developing the ability to reaccelerate after hurdle clearance. Also, running sprint-float-sprint type runs will help because you have an initial acceleration, then relax, and then have to reaccelerate again (similar to hurdling). Also, try running competition spacing but take out every other hurdle which will emphasize the speed aspect of the event more.