1. Scheduling can be gotten around by using MAC OS X's crontab.
I don't know how similar/dissimilar it is to the standard UNIX/Linux crontab, but this is the system scheduler for *NIX variants, and OS X does have a crontab daemon.
2. At least in the standard Linux install avast has a -p arg that defines what automatic action to take. I posted this part of the manpage elsewhere.
-p, --continue=NUMBER
allows setting of an action to be automatically performed: delete file - 1, repair file - 3,
user input - 4
...which suggests a script can call avast in the following manner:
avast -p 3
I've no clue if the MAC version supports this.
3. I'm also looking for the dir/file exclude definitions ability.