As far as keyboard shortcuts go you need to hold option/alt down plus the "show/hide properties" keyboard shortcut to toggle between adding and removing keyframes. Adobe doesn't take the liberty to document them all in their keyboard shortcuts page so here goes:
Option+P: Position keyframe
Option+R: Rotation keyframe (adds keyframe to all rotation and orientation values if layer is 3D)
Option+S: Scale keyframe
Option+A: Anchor Point keyframe
Option+T: Opacity keyframe (adds an Intensity keyframe if layer is a 3D Light)
Option+M: Mask Path keyframe
Option+F: Mask Feather keyframe
Option+L: Audio Levels keyframe
*This only works for single letter shortcuts--double letters don't work (i.e. TT for mask opacity, RR for time-remapping, etc.).
*Option+Shift + the letter will also work which is good if you've remapped the Option+Letter for other things such as launching scripts--which I have.
On the "boomerang" effect, I would highly recommend you go into your Preferences>"General" tab and turn on "Default spatial interpolation to linear" then you can manually add bezier handles to your keyframes in the composition viewer if needs be.
It helped a lot thanks! The Preferences >General tab and "Default spatial interpolation to linear" helped. But also a link gave me another great tip -
If there are 2 keyframes in a timeline choose the keyframe on the left,
ctrl + right click the keyframe and choose >Toggle hold keyframe -it won't move anymore.