Your idea of "trying out" working downstairs is an excellent one. It sounds like you might get a little lonesome down there by yourself.
Otherwise, your proposed space sounds WONDERFUL - :hunf:
If you are in good health and going up and down stairs is not a problem for you - the upstairs stash and downstairs work areas would create "automatic exercise"
If stairs are difficult, the stash on one level and the work area on another would be bothersome.