Yeah curse reduction is for grim, it's effectively additional health when picking grims. Very useful stat, worth getting on a trinket and then just keeping the trinket until you get another with curse resistance, no reason to switch them up while lvling.
For the 15 passives on waystalker, the double one is just twice as much health per tick, still caps at 50% so it's pretty shit, the team one also caps at 50% for your teammates but heals less per tick. Honestly the ammo one is the best by far, because they buffed it last patch so it works even if you're not regenerating health(so even if you over 50%), before it only worked when you were under 50% which made it meh.
Now it's basically ammo ticks every 7 or 10secs or whatever the regen is, and it scales based on the max ammo your weapon has, hagbane is 1ammo per tick, longbow 2ammos per tick and shortbow 3ammos per tick. It's great with the longbow and guarantees you almost never run out of ammo unless you're constantly firing during a very long horde fight(like horde > boss or something and you're just using bow the entire time). It changes the gameplay a lot once you have that passive because you can fire a lot more, can fire at hordes, fire at specials, fire at bosses, fire whenever you want.
Also dwarf starts pretty shit cause ranger is basically a lategame spec. Do note however because it's not mentionned, when you ult, you have 100%crit chance, so you do a lot more damage and can damage armored mobs even with normal attacks(crits pierce armor). Get a shotgun if you can, shit instantly kills specials easily and on bosses you can do big damage with the ult. Once you're Ironbreaker it gets a lot easier to level up. Also for Sienna not sure if I mentionned that but make sure to equip a Fireball or Conflag staff, she can't use the staves for shit she just uses the left click every now and then and those have good left click, but like if she has beam equipped she'll just beam for half a second and do nothing else, which is basically a big waste of time.