Well, hard pruning won't promote heavier trunk growth, but it will cause back-budding, pruning opportunities to create trunk movement if you desire, and the potential for some future taper if you intend to grow the plant as a single trunk specimen. Obviously, you're not going to make a believable looking tree that is 24" tall with a half inch trunk, so yes - trunk chops will be required.

I would wait to repot until you are ready to move the plant outdoors. This will be when nights are reliably above 55* or whenever you're ready to move the tree in and out when temperatures dip below 55*. The tree has good natural genetic vigor, and will begin to gain strength quickly after you move it outdoors. In mid-June, you can cut the plant back hard & allow it to grow freely all summer long, tip-pruning as required to keep the plant tidy. Next spring, you can assess the need to repot again and prune hard again after establishing an idea of what style the tree is leading you toward.

The soil should be structurally durable and free-draining. You can grow it on in a large pot using a coarse mix of bark and perlite or build a bonsai soil of something like equal parts by volume of Turface (or equal), Grani-grit (or equal), and screened pine or fir bark in an appropriate size. An excellent fertilizer choice would be something like MG 12-4-8 or 24-8-16 with micro-nutrients. Remember to add some dolomitic lime to your soil when you make it, as a Ca/Mg source, because many fertilizers do not contain those nutrients and they (like all the others) are essential to growth.

Good luck.

Al

As a tropical, indoors, you can repot at any time. Now is actually a good time. Get it potted into a larger pot for trunk development, and wait till spring to do any foliage trimming.

I would grow it in a large pot for several years to develop the trunk. Chopping it anytime sooner will just delay trunk thickenening. Don't do a trunk chop till you are satisfied with the circumference of the trunk itself. Allow it to develop - that means leaving all branches in place - this helps develop trunks. Taking branches off will just retard development.