Skip the Japanese maples for now. Get decent, mid-level Chinese elm, or native elm (American, slippery, Siberian, cedar, etc.) stock. Don't waste your time on seedlings and saplings, as they will teach you nothing about making deciduous bonsai for a decade. Any elm is forgiving of mistakes, abuse and they grow like weeds in our climate. Bald cypress is another deciduous tree (although it's a deciduous conifer) that is tough and develops quickly here.
JMs are not all that easy for those just getting into deciduous bonsai, at least not as easy as any elm. Elms develop very quickly and can offer a "short-form" course in how to develop deciduous trees overall, as pruning, and design can be used across species.
If you have landscape JMs, you may also have issues with suppression and possibly disease. I have to grow my JMs away from my big landscape Arakawa because if the JM bonsai are kept underneath it, the bonsai lose their leaves by summer. Don't know if that's others' experience, but it's happened repeatedly. Doesn't if I move the bonsai out from under it.
BTW, Tridents are not like JMs. Their resilience is far superior to JMs. Tridents (Acer Buegerianum) are not Japanese maples (Acer palmatum). They are different species of Acer. Trident is an ASIAN maple. Similar geographic origin doesn't make it the same species.
BTW, I grow nothing but deciduous. I find they endlessly more satisfying as bonsai than conifers. Fall colors, fruit, flowers that deciduous trees produce regularly far outstrip the constant green, tedious care and easily manipulated foliage of conifers. You can't "cheat" with structuring design on deciduous trees. They show everything in winter and spring.
