You won't receive the "Legendary in 10" for those sets you have opened previously.
I thought this was pretty clear:
- Players who have opened 1 or more packs from a specific set prior to the change going live will not receive this bonus for that set.
2
Reaching legendary for the first time with a deck tweaked by myself!
1
Just doing my part in making a friendly community :)
2
You guessed it right. You can no longer play it in standard format after the first expansion next year is released.
http://hearthstone.gamepedia.com/Standard_format