... ...root pruned last october 2016 , am I correct?
November the 20th to be precise.
How deep is the overall rootball?
At the time being it is almost 16-18cm. The original rootball had been something around 30cm.
When you were root pruning, did you cut any larger roots?
No. Did not find any. Lots of thin roots, like matting.
After rereading, what I would say is feed and water that thing, let it grow all it will.
I would not do any layering this season, next year if it does well. continue watching and planning................................you'll find it in due time.