In ground What else should I do prior to root pruning

[Japonicus]

If it was mine, I would probably do that trimming and project.. But everybody's taste is different..

On my virtual, i put a "?" because i don't know how is the base and nebari. But for me, if the nebari/base is good, you have a good pre-Bonsai IMO
View attachment 601860

Nice virtual @clem. I see you've kept the right low branch, and windswept the left one.
Thank you so much for the time and thought.
How far out, timewise are you suggesting the chops? Doubt I will do more than 2 side chops or one trunk chop at a time.
Base and nebari are not "good" for bonsai.
The only close to pics of the rootspread is in post 42. Tried to get a pic but ran into a lot of fine roots not far below sorface. Just 1 yr from lifting I didn't try very hard to get the pic.

 

[clem]

How far out, timewise are you suggesting the chops? Doubt I will do more than 2 side chops or one trunk chop at a time.

In my greenhouse, some of my JM grow in summer.

If your JM usually grow in summer, and if you are sure of your project (virtual), you can make the cuts right now because your tree is vigorous + lots of foliage. Cutting now will encourage a second growth and the sun on the trunk will encourage the emergence of dormant buds (future branches), IMO

If your JM doesn't grow in summer (just spring growth), I think it is better to not cut anything, let the tree make plenty of reserves, and trim in Autumn (September-October). It will produce new buds 1 month later, and/or next spring.

It seems like logical advice to me, but it's up to you.