I’m not sure about an elm. I was thinking more like a maple. I did have a sugar maple sapling I was going to train into a bonsai, but it died over winter.Ebay has pre- bonsais , I collected most of mine as saplings, no need to spend $40-50,000 or more on em, even many rarer plants can be had cheap if you look hard enough, or ask the right people.
Why not start with a slippery elm sapling? They have a faster rate of growth which allows you to get an actual bonsai shape quicker, and are hardy as well.
I can grow most things, but trees indoors might be more then I can handle.
I do want to try again. That’s why I was thinking of getting one that’s already been started so hopefully I don’t kill it. Lol