Volume is refered the the amount of space within the mask when it is on your face. The lower the volume, the less of an air space there is, making it easier to equalize the pressure when there is a mask squeeze.
There are many masks that offer a wide field of vision including some amount of peripheral vision. Many divers opt for masks that don't have that feature since they desire to concentrate on what is straight ahead.
The best mask advice I can give is to find one that is a very comfortable fit and seals against your face well. When selecting ANY gear, comfort is your main consideration, since if it doesn't fit well, you won't enjoy your dive. At first, don't worry too much about brands, just try on lots of masks until you find one that fits well. Then once you find a brand that fits your face, then you can seek out the options like purge and side windows.