There's little getting around having to just let it grow until the bottom section of the trunk is as thick as your want. I got about 5 years down the road before it occurred to me that I didn't want it to be arrow straight. You got that much pretty well nixed already. But what you do depends upon your aspirations.
If you want a thin sinewy feminine tree, you won't be worrying much about thickening the trunk nor making it taper - priority will be movement and you'll be chopping it soon and wiring the thin stem from it for movement If you want shohin, you'll probably want a thicker trunk and if you want to get to sumo proportions you'll need a trunk with a lot of fairly close nodes (which may exist somewhere along the existing stem that you can 'harvest' as an air layer sometime). And, yes, you can always air layer to at least double your trees, maybe think about a group or forest planting too.
Finally, keep in mind that every great work lies atop a huge junk pile. Masterworks are one of a kind, but not one-offs. Do what you FEEL like doing and see where it leads. Just don't do the exact same thing with everything you've got. That's the only real advice I have for you.