Thanks for the questions! Let's see if we can get them answered.
1.) I believe that within the current versions of DirectRT, the limit is made up of 99 images per trial. This would mean that unfortunately 100 images per trial would not be possible.
2.) The following may help:
Also, check out: http://www.empirisoft.com/directrt/help/directrt_jumping.htmIf you have stimuli following the jump command on the same trial, DirectRT waits until the end of the trial to jump. If you want a jump to be executed mid-trial then assign a negative value to the trial ID. e.g., To break out of a trial immediately and jump to trial 100, you could indicate rt:44<-210,53<-210. Subsequent stimuli on the trial will be ignored.
3.) Remember to make sure that the image is on the same trial. The screen will automatically clear at the end of a trial regardless of what you input.
4.) Yes. The experiment would be a bit long, as you would currently need jump sequences for every image; however it would be possible. In the 2010 copy of DRT this will be a much easier function to manage.