Trunk thickening is a factor of top growth + time. You can get thickening by either lots of top growth and a little time or less top growth and lots more time.
The problem with lots of top growth and conifers is that most won't bud on bare wood so we must maintain some low growth while allowing lots of top growth so there's something to cut back to when we get to the inevitable chop.
I know you picked the tree because of the curved trunk but the reality is that we rarely end up using all the original trunk in a bonsai. They are more usually developed by chopping to a lower branch and using that branch as the new trunk so much of the original trunk is sacrificed.
Can't help with developing ramification on Thuja. That's a genus I have very little experience with.
