Cutting back

It depends on how big you want it next year. You can cut it back really hard. Any time soon.

Disagree - should be done in spring, not now. You can take a bit off the top now, but not too much. hard pruning now will encourage new growth, which is the last thing you want at this time of year - it'll get killed by frost.

I leave mine until it starts to shoot in spring then you can see what has died back and take that out. Often the long shoots that have grown during the latter part of summer will not be hardened off enough to survive winter. Of course you can cut off any excessive growth then too.