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It's possible there was a tree at one time, but now only suckers are growing.

I don't think that I would recommend growth inhibitors in this case. You would need to obtain the correct chemicals specific to the tree, while trying to prevent it from coming in contact with specimens nearby. I recommend growth inhibitors in very controlled situations.

In your case, This extraordinarily large tree might be best removed by a professional in your area. You could try your local extension service. They may have a few suggestions for people that can help you to remove the tree in your area.

https://www.gardeningknowhow.com/extension-search

Yes, they are hardy in zones 4 to 8. Here is more:

https://www.gardeningknowhow.com/ornamental/trees/catalpa/catalpa-tree-planting.htm

Yes. This is typical of the Catalpa. Being incredibly large trees, they will stretch the trunk and appear bare as it prepares to be a trunk. It is worth noting that they are extraordinarily prone to falling apart and breaking. I wouldn't let it branch out much. It is meant to have a singular trunk that is straight up. Any main shoots that make their way at an angle Can fall over and break as it gets older. So be sure to keep any competing branches from the base pruned out. Some recommend pruning once the tree starts to get too tall to reach. While this is nice for shape and structure... it can become a hazard, later, unless you prune constantly to avoid larger, more mature branches.