Good luck, I have 5 years OTR heavy haul experience with a perfect record and they won't hire me. I think you have to know somebody who knows somebody over there.
As far as I know you have to work your way up the tiers... Specialize is Lvl4 then lvl3 and so on... Every tier has its restrictions of how much you can OD haul... Sorry I don't know the specifics. In the four months I work with them just before the holidays I hauled OD loads... I needed 3 more to get lvl3. I could only haul 10f W legal height.
Forget trying to work into heavy haul with ATS, I was there. Part of the reason I left was because they won't work you into a position (as they promised), they only hire drivers from other companies to work heavy haul.
During orientation they will teach you how to hook up, remove the neck and reattach. That's about it. They provide instructions sheet in your permit book as well if you forget. During class they will go over securement etc. Theres also a number you can send pictures to if you have a load you aren't sure about how to secure it they'll advise you based off the info they have. Now any other ATS driver here with longer tenure with the company may have more information than I.