I think its a sango kaku but I am not sure, its my first bonsai, and has lived through alot of bad mistakes potting, pruning in the spring not fertilizing for 2 years, improper winterizing. I definitely think Acers make great starting trees for bonsai
Might be sango kaku but could just be basic variety. The growth habit does not look like sango to me. The leaves and trunk look like basic green maple. Sometimes the have some red in early leaves and trunk can have some red too.