About summer-bearing raspberries.

I have cut out all of canes that bore fruit this year (floricanes).
Can I shorten the rather straggly new canes (primocanes) to a manageable
(i.e. tidy) length?
Or should I wait till next spring?
I plan to cut to 120 cms in the spring to encourage side shoots where
flowers/fruit will develop.
Is this a good plan?
If I cut them now will fruit grow on the new growth that will develop above
the cut point?

There is SO much about raspberries - I need some simple rules!
Thanks.