Hello. I am working with Sony Vegas. To change the speed, just right click on your video sequence > properties > read frequency (something like that, its a google traduction) is normally at 1,0000, this is the speed reading, you can change it. If you want very slow motion, you need Twixtor pro.

Keyframes, do you think about Toribash keyframes or ? If its for Toribash, pause the game, put a key frame, unpause the game, pause it again after a few frames, keyframe again, etc. The keyframes create directly a path for the camera, with a bit of training, you will be able to know how the camera will move between your keyframes.