OK, so I saved an azalea from the curb last spring....not sure how old it is but it has two base 'trunks' that are 2-3" in diameter. I placed it in a concrete pot that is ~14in diameter and tall (16in). As I had all intentions in eventually making this specimen into a full bonsai, I made a very porous soil mixture to pot it in (but not actual bonsai soil). I cut back all the branches to a canopy of 15-18" diameter - this was from a pretty mature bush at 3' across. The plant did great this summer and all the major branches have great foliage on them again (the new canopy is very full). So my question is about timing and pruning/repotting recommendations to finally moving this into true bonsai pot (plan is 12in diameter with 2-3in depth). I am worried about cutting the main roots to make in fit in the shallow new pot. Can I cut the bigger/deeper roots in the middle to encourage larger root growth laterally (to make a better nebari) or is it better to sort of coil and stuff them in the new pot (and wire the tree down) to induce less stress. My original plan was to leave in current pot this winter and wait until after it flowers in the spring to repot. Then a little later really prune into a more desirable shape after it had time to recover from the repotting. Now, I am kind of wanting to repot it soon, I'm in Memphis and it will be mild this fall (also, I can move it to the carport so it will be next to the house) and letting it flower in the spring with a good pruning after that. Thoughts?

Picture one is after first month in new pot and major pruning
Picture two is a month later, currently the plant has about 20% more foliage

I dug up several large old azaleas two years ago, put them in large pots, left them for a year, put them in smaller pots this spring, and plan on serious pruning next spring.

My advice is leave yours in the pot you have it in for another year and don't prune next spring. Being dug up and left on the curb is a pretty big shock. Let it recover.

Once it flowers, as blooms start to fade, cut them off. This will encourage more flowers.

So once I hit the end of year one: then repot but not prune? What about a plan for pruning roots when it does get to that time? All the info I found for bonsai pruning is for when repotting into a similar or larger pot (with ~15-30% reduction at the root edges). How did you do a major pruning down without hurting the tree? Just cut down the shape to fit the pot directly? In a typical bonsai pot that is 3-6in deep this would be some serious cutting to major roots. Would it be better to try and retain the larger roots and coil them around at bottom of pot or do I need to suck it up and cut them down?

Rather than curling the roots use a larger pot, then at the next re pot reduce the roots more. The time to re pot Azaleas id either in spring or after flowering. With this plant only just dug I would stop it from flowering next year and re pot the following year. The top can be pruned hard and it will bud. Bear in mind the Azaleas are basally dominant so prune the apex less than the base.