Wow, how did you loose your avocado tree over the summer?

You can trim the long wild blackberry vines back now, and then a big pruning in February.

I'm not sure on the fertilizing although I don't see how it could hurt.

I don't know about blackberries specifically, but all my landscaping/gardening books/magazines/websites say that now is the time for the last feeding of fertilizers for most other plants. Doing so any time after October is a good way to suffer cold damage to young growth.

I've grown barzos blackberries in the past. This variety grows in a semi-bush form. As recommended, I would cut the growth down to about 5 inches off the ground right after fruiting, in May. That way the plant has all the rest of the year to become a sizable plant again. If your vines "are all over" they may supposed to be that way this time of year.