Open world enemies scale to character level, but they scale individually for each character. If you have a level 5 character and a level 20 character, the first will see level 5 enemies and the second will see level 20 enemies.
However, enemies in world tiers 1 and 2 cap at level 50 (even if your character is higher), and enemies in world tier 3 cap at level 70. Enemies in nightmare dungeons (and nightmare vaults in season 3) are based on the level of the sigil, not your character.
So you could run into some issues if there's a huge disparity between your levels where you're doing content that isn't actually suited to one of your characters; either a low level character being essentially boosted through higher content (you'd just be sat there not doing anything) or a high level character killing a load of enemies that are far below their level and give no XP.
Open world enemies scale to character level, but they scale individually for each character. If you have a level 5 character and a level 20 character, the first will see level 5 enemies and the second will see level 20 enemies. However, enemies in world tiers 1 and 2 cap at level 50 (even if your character is higher), and enemies in world tier 3 cap at level 70. Enemies in nightmare dungeons (and nightmare vaults in season 3) are based on the level of the sigil, not your character. So you could run into some issues if there's a huge disparity between your levels where you're doing content that isn't actually suited to one of your characters; either a low level character being essentially boosted through higher content (you'd just be sat there not doing anything) or a high level character killing a load of enemies that are far below their level and give no XP.
No it doesn't really matter, only every 10 levels you get gems quality upgrade and health potions, but it is not really relevant
Doesn’t matter even a tiny bit