I have had a lot of these types jobs pass through our shop recently.
Some tips I think you might find usefull…
Things to check before exporting as .ma that can cause issues :
Convert your scene from cm to mm before export to .ma, or just have a very large scene to start with. This is because after effects measures scene units as pixels… if your scene is too small in scale inside maya it can cause some transform disparities between the comp and 3d scene.
Make sure your camera is set to your goal comp resolution in your render globals
aswell as making sure your primary render camera is set to the camera you are exporting.
Your scene FPS must be set to the same as your target project in comp.
Make sure your timeline is set to the exact frame range of your project.
For static objects you only need one keyframe at the start and one keyframe at the end of your sequence timeline, this will help reduce filesize.
As for animating the focal length you can work it out.
In after effects you can change the size of your camera’s film back which is in width by height, this directly affects focal length. In maya if you look under the Film Back rollout of your camera’s attributes… you can get a film back measurement under Camera Aperture… note this measurement is in inches so when you take into Aftereffects if it gives it to you in mm do a conversion first. And I believe you can link the vray physical cam attributes to change the maya camera attributes and then could translate the measurements into after effects. I think the hard part would be matching the animation curves if you have an eases in your focal length changes.