Personally, I prefer a larger area, but everybody has other preferences. So you should try some more areas, but i would recommend to stay with one, when you have a area that feels comfortable for you.
Depends, I used to own a Huion 420 and i had a VERY small area, one where you almost can't see even my fingers moving. Then i switched to the G640 and i got a larger Area(still small for some people though) and after a week i got used to it, it's basically just another preference situation