Thanks for the great advice Bonsaitrees! Your virt cuts were exactly what I had in mind.
So yeah, before I read what you wrote....I repotted it this afternoon!
I just felt like the tree was that rootbound/compacted...when I would water it the water would stand on the surface of the soil for up to half an hour! So I felt like that was more important than a hair cut. If I've missed my window to give it a hard prune/style, I'm happy to wait til next year.
So I had to cut the pot off it with a box cutter and was greeted by a nearly solid mass of roots. I used a saw to cut about 20% off the bottom, and then tried to tease out what little soil was in there. I also tried to trim out the fattest roots...though the root ball is still WAY too big compared to what it will need to be to get it into a bonsai pot one day.
I've put it into a slightly larger pot than it was previously in and watered it well with Seasol.
So now that's done, how long should I wait before a hard prune?
And how should I go about cutting the main trunk? Should I cut it at an angle so the scar will be towards the back? Never done anything like this before.