I also think it may probably be a Norway Maple rather than a Sycamore (Sycamore's tend to have a 'toothed' edge), it's also a non-native but generally less invasive so perhaps you don't have to worry about being kind to it! I think the pot is fine, as commercially, trees two and three times that size come in pots smaller than that.
In answer to what you can do for it, probably you don't need to do too much, if you just wait and watch you'll probably see it gradually callus over the wound, and if it's of any relevance, guerilla forestry may be a good tactic whilst you save up to buy your land - just remember right plant, right place.