The Hero and Vanguard classes in fates are different both in stats and the skills you gain from it. They are not the same class with aether added in for vanguard.
If you're referring to dlc from map pack 1, it does. I bought it for the special edition and was still able to access it on my conquest cartridge. If you're referring to the path dlc though idk. Though I assume if the DLC map packs are compatible across different cartridges buying paths may be compatible as well.
Where does it say you HAVE to buy both physical versions to get the bonus, I see the bonus on their website for their bundles that are one physical route+the other route as digital for 60 bucks as well as just one physical on their own for 40. And the link you sent doesn't even say you need to preorder both physical.
Edit: I forgot to glance the ad itself on the link, but it seems more like a misunderstanding. the actual preorder doesn't seem to imply that you need both it just means you can get it from preordering one or the other.
I'm gonna assume your confused as to how the stat caps don't match the ones on the site, its because theres a feature in my castle where u can set up statues that raise the caps of characters
theres info at the bottom of this page.
http://serenesforest.net/fire-emblem-fates/my-castle/buildings/
The Anna map is out, and anna seems scale with chapter progress as well. She's a lvl 18 adventurer with all stats caps at endgame.
Edit: It's only for the map though, when you recruit her, she's at her base stats.