As I child I had absolutely no clue what I was doing, but now I am much more interested in the actual art of bonsai
Great that you managed to keep this tree alive since your 14th and for such a long time.
However, I noticed you do not like rude answers, so I apologize for the next part of my comments, as you're not going to like it: If you are really interested in the actual art of bonsai, get another tree.
This is not a real bonsai. A bonsai is a a miniaturized version of a tree with the characteristics of a real, full grown tree.
Your tree lacks all these characteristics. As you already wrote, "you can clearly see the scar where they clipped off what looks to be the central trunk". This is NOT done "in order to make the plant a bonsai", but in order to, in a short period, make something that LOOKS like a bonsai. I agree that your tree is 'just a ficus', with a cut trunk.
In real bonsai, trunk cuts are done too, but techniques are used to create a tapered trunk with no visible cuts. This takes many years of growth and training.
Home Depot does not sell real bonsai, they sell what's called mallsai - mass produced, young plants that are made to look like bonsai in the shortest possible time. There's no art involved there, these trees are all made the same way using simple techniques, they are not unique, they all look the same.
Indeed you should not have defoliated your ficus. It's no use and will do no good. Defoliation is done on established, and very healthy, bonsai only. Your ficus needs its leaves to grow.
Wiring this ficus and putting it in a pot will still not make it a bonsai. The thing hardly has anything to work with.
To try and make something out of it, you will have to let it grow - a lot. Make it thrive, let it develop branches and leaves.
This will take a few years, and then still it will probably not be very good bonsai-material as the base isn't very good.
So, get another tree. Don't buy another mallsai, but buy starting material from a (bonsai-) nursery. Before you do, learn what good material is, how to care for it, how to make it thrive. Then start learning bonsai techniques, look for examples, maybe join a club. That is, if you are really, as you write, interested in the art of bonsai.