Will the people of Paradise envy one another, or feel غبطة (a wish to have what someone else has without wishing them to lose it), or regret their shortcomings in this worldly life, despite the varying degrees of their stations therein?

The people of Paradise do not envy, nor bear malice, nor grieve. They admire one another's state, and their admiration means approving of their condition. As for the narration about regret over a moment that passed them by in which they did not remember Allah, it is understood to apply to the موقف (standing place/situation) before entering Paradise. Once they enter it, there will be no regret or sorrow.