In your play, F5 straddling 3rd may or may not be obstruction. 2 things have to happen to be obstruction, the defender doesnt have the ball AND they impede the progress of the runner. If F5 straddling the bag cause the runner to pull up or slide, that would be obstruction. But, if the runner slid because there was a play going to be made at the base and it was just typical playing action and the runner was not impeded, then no it is not obstruction.
As for running into and tripping over F5 straddling the bag without the ball, yes definitely obstruction but no it is not necessarily a "free trip home". The only guarantee obstruction gives is that a runner cannot be put out by the defense between the 2 bases where obstructed. If the runner is put out between 3rd and home, the umpire will have to make a judgement as to if the runner would have reached home safely if not for the obstruction. If not, then the runner would be placed back at 3rd, if yes then they are awarded home.
As for running into and tripping over F5 straddling the bag without the ball, yes definitely obstruction but no it is not necessarily a "free trip home". The only guarantee obstruction gives is that a runner cannot be put out by the defense between the 2 bases where obstructed. If the runner is put out between 3rd and home, the umpire will have to make a judgement as to if the runner would have reached home safely if not for the obstruction. If not, then the runner would be placed back at 3rd, if yes then they are awarded home.