Here it is a very fast grower and a seedling can fruit in 3 years.
Don't know about cold hardiness.
I've been through a few generations with these and it seems that, at the moment, I am getting fruit set on all 3 trees that I have. Before, I always had at least 1 male. About 3 years ago I planted 3 new trees to add to what I had left which was 1 male and 1 female. The male died,(these trees don't last so long), and something happened to one of the newly planted trees. As far as I can tell I now have 3 tree grapes producing fruit and none not producing.
I've never grafted anything like this. I would think you need to plant more seedlings.
Peter