Any time you want. Just advertise in the 'friendly cups' forum section and you can try to get started from there. Now would probably be a good time as plenty of people start friendly cups at the start of a new season.

There are plenty of people looking for teams to join their own friendly cup too.

After the last game of this season, there is a weekend with no fixtures whilst everything is re-set, then the week after the new season starts.

In one of the forums, there is a guide through the off-season relating to the dates fixtures etc are released, but I've found this has been different the last two years so don't pay too much attention to it.

The part regarding wages is most important.