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Yes, it should be okay to remove the pot, and I would actually recommend that you do so. In fact, it may need to be replanted into the ground or even placed into a larger container. To transplant the tree, this article will help: https://www.gardeningknowhow.com/plant-problems/environmental/learn-how-to-avoid-and-repair-transplant-shock-in-plants.htm

This article should help: https://www.gardeningknowhow.com/weed-identification-control/weed-trees.htm

You can but there are certain things to consider when growing trees in containers. These articles will provide additinal information as well as other tree suggestions for future reference: https://www.gardeningknowhow.com/special/containers/how-to-grow-container-trees.htm
https://www.gardeningknowhow.com/ornamental/trees/tgen/growing-trees-in-containers.htm

Are the stems (branches) still green? This article will help you determine if the plant is still alive: https://www.gardeningknowhow.com/plant-problems/environmental/how-to-tell-if-a-plant-is-dead-and-how-to-recover-an-almost-dead-plant.htm

Fall is a good time for transplanting. If you cannot do so now, then spring would be ideal. Get as much of the roots as possible and replant in a suitable location. In order to reduce the amount of stress on the plant from moving it, you may want to consider cutting it back. This article will also help:
https://www.gardeningknowhow.com/plant-problems/environmental/learn-how-to-avoid-and-repair-transplant-shock-in-plants.htm

Depending on variety of maple, you may not be able to be root free above ground. Some maples have more prominent roots above ground than others.
As far as the locust is concerned, if it were mine, I'd purchase an herbicide with 2-4D as an ingredient. Immediately after cutting back a sucker, pour a couple tablespoons of herbicide over exposed stem. This should kill the sucker and any others along that particular root/rhizome.