3 years in that pot means you'll probably want to repot it this spring.
If you plant it in a bonsai pot, you won't get 4' of growth.
If you want to shorten the two main branches, repot it into another grow-pot and let it grow freely to get some good taper from the branches that will emerge from the cuts.
Hard to cut your own tree, but the first thing I noticed is that the main 2 branches off the trunk were too long, and that will ALWAYS be an issue if you don't address it. It might not seem like a problem now, but in 5 years you'll probably wish you did it back when you first got the tree. Then it's going to be REALLY hard to cut off all the growth you've painstakingly grown!
Mine is really bad right now, but it has potential that maybe only I can see! I cut it back from a 4' tall slant-style tree that never looked good. Ben Oki did the original styling back in the early 90s. When I cut it down to 18" stump, it also had no roots on the left side of the tree, hence the small pots. New growth never appeared on the right side above the halfway point on the trunk, so I thread-grafted branches in 2008, and they still haven't taken. Here is a progression over the last 4 years...