Wow that's a fast growing tree! What species is it? I wish mine grew so fast :-) it's cool because in case you mess up, the tree will recover fast.
Growing a tree from seed is a very interesting project and you could learn a lot in the process. It would create a special bond with the tree, too.
I don't know a lot about bonsai at all! I've only had them since January. I learn in the process from my mistakes. For example, I didn't cut off the branches where the buxus had dry leaves hoping they would regrow. But they didn't for 4 months. Finally, I cut them off a month ago and new leaves started growing on other places soon after that.
So far, my trees were inside in the winter, than I moved them on the window from the outside side and after that, they went on terrace in the garden. There was too strong sun on the south - east window as summer approached.
I will post pictures tomorrow or on Monday because I'm at our garden (1km from home) and I only have mobile here and I have no idea how to insert pictures here on tapatalk