resolve when skill proficiencies overlap (for example, getting Stealth from Street Urchin background + get Stealth from Lightfoot Halfling should resolve in me getting to pick another skill proficiency instead)
This is one that really annoys me as is. Under PHB Rules (Chapter 1: Step-by-step Characters pgs 11 - 14) Background is the one of the last element of your character to be selected (after race and class proficiencies have already been selected), and selecting a background with overlapping skills/proficiencies for your class/race should grant you access to a free proficiency from ANY skill (not just those on your class list - pg 125 PHB "Proficiencies"). E.g your Lightfoot Halfling Rogue gets Stealth from his race and can then choose to take Acrobatics, Deception, Investigation and Slight of Hand from his class giving him 5 skills in total. If he then selects the Criminal background, as the game stands he gains no additional benefit from his background and only has the 5 skills he already had selected, in 5E, as he had Deception and Stealth already from another source (and technically also has Thieves tools twice...though that and other tool proficiencies are another matter entirely) he in effect gains two free-choice skill selections from the whole skill-list, letting the player customise their character beyond being just a criminal who stabs people, maybe taking Nature and Survival to fill out their background as having lived as a bandit for a number of years, or Religion and Medicine to cover the time they hid out in a Monastary to get away from the law.