Sadly it only applies to the character you do your first completion of the objectives on per season. So you did it on WD this season and that means any new character you create won't be able to get a haedrig's gift...until next season
The season journey will spell out exactly what you have to do and what rewards you get (Shift-J on the PC).
I know you get all 3 gifts (2 set pieces in each gift) by the time you finish chapter IV (4). It's all pretty basic stuff (even the set dungeon task- a lot of them you can literally just walk in and let the time count down without doing anything and get the achievement... or just slaughter everything and get it).
I did the seasons journey tasks on my DH and then leveled up a Sader and opened the gifts on her to give her the full invoker set.
Edit: Apparently, you can get the bonus set just by doing those tasks mentioned in the OP's post. My apologies for any misinformation towards answering the OP's question. I was speaking only from my direct experience.
I wasn't aware you get the sets outside of finishing chapter 4 in the seasons journey. My apologies for any misinformation towards answering the OP's question. (added edit above too for new readers)
So that means you can do the achievements in SC and then just level up a toon in HC and have a full HC set? If so... I understand the complaints about it, but that is an amazing way to jump start playing in HC. You hardcore folks should be handing out the HC kool-aid.
Sadly, if you got the set in softcore, even if you gear another char in hardcore, that other char will not get Haedrig gift.
So, it is only once per season.
yep, seems so. leveled up one hardcore char, ready to crack some skulls with the might of the earth.. nothing in the mail. haven't claimed the three gifts from my SC chars, why aren't they REALLY account-wide?
really bums you out, you know..
edit: and to be clear: hardcore isn't that hard. you can still get boosted, you can still leech your ass off for shards and lucky drops in public games and you can still receive a full set rather quick. so it wouldn't hurt the community if some blokes got a free set out of their efforts.