Are there certain limits that must be observed regarding good character, the bounds of beneficence and ignoring people, and dealing with those who exploit one's kindness and become accustomed to receiving good from them, or should one continue to do so regardless of others' reactions?

You are upon immense good by forgiving people, overlooking their faults, and being kind to them, even if they wrong you. So, continue with this virtuous character. Know that Allah will not let your reward for this good go to waste. Allah Almighty says: (Indeed, We do not allow to be lost the reward of any who did well in deeds). There is no harm in taking a firm stance, in a good way, with those who try to insult you or infringe upon your rights, by stopping them at their limit.