i don't know of a way to hide them (like soloing a layer), but you can lock the masks you aren't working with to avoid changing them.
you can also color code them -- clicking the colored square next to the mask in the time line will bring up a color picker to change the color of the mask path.
you can also set ae to automatically set different colors as you add new mask paths in the appearance preference (check the option for 'cycle mask colors'). it will only effect new masks, not the existing masks, but you might want to enable that option as you continue...
Lock the masks you want to hide, then go to Layer -> Mask -> Hide Locked Masks
Johnny Cuevas, Editor
"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.