A8
First off, the spell is horribly written. There are a lot of issues and the spell doesn't work according its school and subschool. There is no disbelieve even though its a illusion spell and it deals damage even though its a glamor. So by the normal general rules this spell cannot function, so let's treat it as a complete exception and answer your question as best as the spell allow it.

The wisdom damage (and fear effect) only applies once, when it is cast and nothing states multiple rounds. Compare to Cloudkill, who does deal damage over time.

The caster is not immune to the damage. There is no disbelieve to prevent damage. (This comes back to the fact it doesn't function like an illusion spell and especially not as a glamor spell.)

A 20-feet radius, so the spell will always look like this: picture.
It doesn't matter where it is cast, you pick 4 squares (technically the center of 4 squares) that fall in reach of the range (20 feet) and the spell starts at that point.
This also means the caster is always in his own cloud, at best he stands on the very edge.

If you have more troubles with the spell; a simple Google query will reveal tons of Paizo forum topics about it or start a thread/PM me and I can link you to the better ones.