Hi Denise. In the gallery above I loaded a picture of one of the original plants at the Buchholz Nursery. As you can see, it will get quite large over time. However it takes nicely to aesthetic pruning and shaping. It's your call, but I think this tree will overwhelm your space after 20 years.
thanks for the update. The information you provide is allowing us to be well on our way to completing the record on this one, but it's a little vague. Do you know who found the original broom, when and where in NY state? This concerns me a bit because 'Miss Grace' is eerily similar to 'Bonsai' and I understand that 'Bonsai' came from New Jersey. It would be a bit of a disappointment if they were simultaneous introductions of the same plant . . .
I don't have a confirmed record on who found it. I've attempted to contact Talon regarding this with no luck. Below is also a link to his blog which also mentions that the discovery was in New York State. I do not believe they are simultaneous introductions. 'Miss Grace' was discovered as a Witch's Broom, where 'Bonsai' is a seedling.
<a href="http://florawonder.blogspot.ca/search?q=miss+grace" rel="nofollow">
Buchholz Blog on Miss Grace</a>