I'm new to this bonsai game. I'm not new to gardening, I have a fair idea what I'm doing when it comes to veges and household gardens. But I reiterate, I'm new to bonsai

I've recently got a few small plants (saplings and root stock) such as Chinese elm, Japanese maple, cotoneaster etc and I have taken cuttings to grow of my favourite trees around my house. Long term my goal is to grow these trees and to learn the art of bonsai.
With these baby's planted and growing happily, I twiddled my thumbs a bit, and got reading and watching some YouTube videos which gave me the idea to chase some older nursery stock to add to the collection to speed up the process a bit.
Now I don't have a bonsai nursury in town, so I've been scowering the nurserys and I came across (what I thought) was a magnificent lilly pilly (as well as a crepe myrtle but that's for another post).
From what I was told by the staff, it is about ten years old and has been left forgotten out the back for that entire time. It's in a 20 inch pot and was a out 3 and a half feet when I got it.
Here are some pics from when I got it home and took the main trunk down and trimmed a few of the long branches away.
My plan so far is
1: cut the main trunk down to about an inch above where the three branches leave the trunk.
2: of the three branches, wire the left and right one to the sides and leave the middle one be as a new trunk cutting it a few inches up from the junction.
3: trim said wired branches, left branch longer over the exposed roots and right one a bit shorter
4: leave the lower branch for a bit to see if it will work well with my design, leaving it untrimmed for now to thicken it up
5: trim roots a bit and repot in the same pot with new soil
The plan from there would be to leave it grow out in that pot for another year then repot into an appropriately sized bonsai pot.
Am I on the right track or do I have I no idea?
Is it just a terrible plant not worth my time?
Cheers, hope you can help! I'm open to suggestions too!
Dan