There's lots of different roads that all lead to bonsai.
Growing out is just one way if you specifically want a thicker trunk. Nobody has yet mentioned you'll need to allow 5-10 years to develop that trunk in grow boxes depending how big and how well you care for it. They have also not mentioned a number of things that could go wrong along the way so please don't think growing a tree this way is 100% certain.
Some people are quite happy with a smaller tree and not so worried about real thick trunk. This one already has a nice trunk so would suit a smaller, thinner trunk bonsai too. For this I would get rid of surplus branches so the tree can redirect resources to the chosen branches then continue to grow and trim to develop branch ramification. You could see a reasonable bonsai in 2-5 years following this avenue. There's still things that can go wrong following this method.
There are other methods but these 2 are probably the most commonly followed.
Good luck with the proj I didnt want to offend any others options that are trying to help because of my lack of knowledge. But yes, Im very happy with how the trunk movement is and I would love to trim out some of the un-necessary branches to make it more visually appealing as I'm growing everything out. I just ordered the 10x10x7.5in, akadama, pumice and lava stone and searching up for fertilizer. But mainly I would like to enjoy it at its small growing stages. Thank you for your comments and hope I can learn more from you! Have a great night!