If you are new to AE then you need to start here to learn how it works: Basic Workflow
What are you trying to do with your high frame rate movies? If you just want to slow them down so you see slow motion then you can do that much faster in Premiere Pro. AE takes time to render previews where Premiere Pro does not. The trick to making this work faster is to interpret your footage at the frame rate you wish to use for playback. IOW your 120 fps footage will be interpreted by AE at a maximum 99 fps. If your comp is 29.97 (basically 30 but standard) and you interpret the footage as 29.97 then 1 second in real time will take 4 seconds in comp time to play back and you'll get slow motion. If you want to transition from real time to slow motion then you'll want to use Time Remapping in AE or use speed changes in Premiere Pro. If all I was doing was making slow motion footage I would do that in Premiere. If I needed more control over the slow motion I would do it in AE.
We are trying to capture/measure locomotion of our subjects. Previously, we tried 30fps which resulted in very blurry images during playback. 120fps has enhanced the clarity of our images, frame per frame. I will try to readjust the comp's frame rate during playback. Another reason why we have used Adobe AE is because we utilize a GoPro and need to correct for the fisheye.
Thank you for your thorough reply!!
Go Pro Studio will remove the distortion when you import Go Pro footage. That's what I do. It works much better than trying to guess at the distortion in AE.
If you want the video to playback in slow motion just set the frame rate in the footage interpretation panel by selecting the footage in the Project Panel and then going to File>Interpret Footage>Main. If your comp is 29.97 fps then interpret the footage as 29.97. If your comp is 24 fps then interpret the footage as 24. You'll get slow motion. If you want to speed it up so one second in real time = one second in screen time then use Time Remapping in AE or adjust the speed in Premiere Pro. Unless you're doing some other effects I would probably do the entire project in Premiere Pro.
In the project panel in PPro select the footage you want to re-interpret, right click and go to Modify>Interpret footage.
In this example I'm slowing down footage shot at 59.94 to 29.97 to give me half speed slow mo.
The result is instant real time playback and editing in Premiere Pro. Much better tool for simple slow mo than AE. All I have to do is create a new sequence from this footage and everything is good to go.