Damage reduction as a whole seems to have been tossed out of the window this edition. There are still elemental resistances but that's about as fancy as it gets. Which is a shame. Killing a skeleton by shooting it full of arrows is still a weird scenario for me.
I think it's part of the whole streamlining thing. Instead of having +2 prof, +3 ability, +1 Circumstance, +2 magic, +1 feat, +4 cheating, etc. you just get advantage/disadvantage (and a couple of those stick around). Instead of resist 5, vulnerable 7, you just take half damage. Instead of figuring out if the colossal dragon is flanked, you just need an adjacent ally.
Though it's also made to be pretty modular. Miss the old flanking rules? Bring em back. Want to use squares instead of feet? I'll bet you assumed squares were the default already. Though on the other other hand, some care should be taken, especially with numbers, given they tried to keep things really tight in this edition, so even a 20th level character has to be somewhat concerned with that horde of 20 kobolds. But it's your game, you can make skeletons take half damage from piercing or able to heal by discussing the finer nuances of Chaucer, or immune to all damage not dealt by people holding the Eye of Vecna (though the latter might get us all killed).
I think the only real taboo is messing with the players' abilities. You can still do it, but it's kind of a dick move to be like "hey, you know that class feature you kind of built your character around? Well it doesn't work on oozes, undead, constructs, Bob from accounting, humans who've eaten dairy in the past 24 hours, or business majors. Because flavor." Though I think that could be done if it was discussed with the player and perhaps gave them something else to compensate.
Of course, that's all just my personal thoughts on the subject, so make of it what you will.
I can run 30 ft and make a ranged attack of 20/60ft.
Can I run to I12 and make a ranged sneak attack?
Yes. Note that lvl. 2 Rogues can use Cunning Action to use Dodge as a bonus action, so you can actually use a melee sneak attack this turn.
I think you mean Dash (/nitpicking)