I assume you mean track motion, since video FX don’t have movement….
in track motion, look for the 2 icons along the top – both have a small lock icon with either an X or Y
one prevents movement on X axis, etc etc
for image size, I usually have no problem with images double res, and seeing as I use PAL, around 1440 x 1152, for panning/zooming. All my text made inside vegas I always set to that res, to increase sharpness / crispness. A commonly used trick.
🙂