In the end you will most likely want a tree on its own roots. Meanwhile, this just needs to grow and thicken up a bit.
BUT, you could try to root some cuttings this year. You only need a couple of nodes per cutting. As hardwood cuttings (gathered now, before bud break) it is better to have a node at the base of the cutting. If you wait until after the first push has hardened (Apr/May) you'll have softwood cuttings that have a better chance of rooting in my experience and with them you don't need a node at the bottom of the cutting and just one leaf will do. It will not tax growing this tree if you strike something like 6 of each type. If any of these root you will know that this tree will layer easily (i.e., you might be air layering next year '22).
BUT before you start hacking away at it, you should give some thought to what style of bonsai you want to make of it. I like clumps and that mess of branches coming from the first node could be a good beginning. If you like this idea, you want to keep all those (--> gather all your cuttings from the branch tips) AND you will want to eventually air layer just below that node. It is very troublesome to cut an air layer girdle as close to a knob as one needs to make a good clump, so it might be that you air-layer it from the root stock in '22 or '23 then build up the roots the following year and then ground layer (in '24 or '25 resp.) to get it done.
IF this is the plan (a clump) and you were to just let it grow, you would have a bunch of straight branches = ugly, ugly, ugly. To wind up with ones that wiggle (have movement), you've gotta cut 'em.
I suggest pruning back no further than to a visible bud (pair) or existing leaf pair. At this point in development, hard pruning won't set it back much (bear this in mind when gathering cuttings).
I would cut all the branches back to varying lengths now, before bud break. You should notice that more buds will become subsequently become visible - you can cut back again IF you want a shorter branch.
You can try to carefully wire the new shoots (Apr/May) to achieve some movement in the internodes. This takes a deft touch. Try one or two. If you break them in the process --> softwood cuttings. HOWEVER, this new growth is what powers thickening, so you want to keep all that you can this year.
yadda, yadda, yadda
Think it through.