You're in for a lot of pain. So have big patience.
I myself have scraped everything possible on retail wotlk heroic and hardmode, big part of it even before the big nerfs, like Firefighter, 3xKnock on wood, and etc (those who remember know most of icc is joke in comparison, especially considering the gear available) in Ulduar, togc25 and including realm 1st lod but here nobody gives a F ;)
People here, especially those in the lod-farming guilds just love to repeat how here everything is harder and you clearing everything on retail means nothing ;) Possibly too scared to lose some kind of credit.
And god forbid you ask something because you're rusty and you've forgotten quite understandably 11 years later, you're handled like a noob so much to the point of being sorry for asking. And if you mention the above be sure everyone will be just waiting for you to fail something and **** on you. Speaking for Lordaeron tho, don't have a clue for the other realms.
So prepare for a long journey and good luck ;) There are many good guys and you'll be surprised how close to retail it is