1) Let Avast! automatically connect every 4 hours is not possible
Depends. Avast checks for updates as soon as a connection is made. After that every 4 hours. But only if the connection stays open. If not, Avast will check again on the next connection. So your calculation is totally wrong.

Only thing you have to do is setup your network correctly so that Avast works on every comp, or use the network edition.