Yes, retail = BfA+all prior expansions. It used to be (back in... Mists of Pandaria or Warlords of Draenor?? I forget) that you had to buy all the expansions one by one, starting with vanilla, adding on burning crusade, wrath of the lich king, etc, but right now if you were to only purchase game time, you'd get access to everything up through Legion. (This will change when Shadowlands is out to be everything up through BfA.) The only reason the Blizzard writing on it says Battle for Azeroth + all prior is because there's no purchase of WoW you can make that locks you out of individual expansions - you're not just buying access to the BfA content, you're getting Legion content, Warlords content, Mists, etc.
The 30/60 days of game time is Real Life time where your account subscription is active. Without the subscription, you can play for free from 1 to 20 (might change when prepatch hits), try out most of the classes, see what you like. With the subscription, you can play death knights & demon hunters too, get past level 20, and explore Azeroth (and the Draenor's beyond) to your heart's content... up until the RL time expires, at which point you'll go back to that "play for free from 1-20" model. If you bought 30 days today, oct. 4, then your subscription would run out next month, nov. 4.
People speculate that BfA will become part of the standard subscription either with prepatch (oct. 13) or with the actual Shadowlands release (current date unknown, but sometime after Oct 27.) So, if you just wanna install the game, mess around at low levels for a bit, and see if you actually want a subscription, it might be an easier way to get started than buying everything in the shop. When October 13's stuff releases, one of the new things is a starting zone (for level 1-10 players) called "Exile's Reach", which does a way better job of introducing players to game mechanics and gameplay expectations than any of the other starting zones - would recommend checking out Exile's Reach, regardless of how you decide to spend your money.
And hey, if you have more questions, I'll be here. Good luck in Azeroth, have fun!