Is there a standard/best size for the gaming area?
80x80 cm is about as much as you need to start. Depending on the final size of your table, you might want to go up to a 1 x 1 meters, but that should be enough.
Or in inches, to start, i think you need about 30x30", to play a 4-5 minis squad (its similar to 80x80 cm).
I use a table of 120x120 cm², but i think that it is too big enough. But, of course i am thinking in huge gangs matchs for the future. :D