Did anyone ever say in which location do we start the game? Do we start at the top of the map (North) in Scosglen and work our way down to Kehjistan in the South? Or can we start at any location? It seems to be from the North to the South. Also when we go to the burning hells, under which area (region) would it be? Which region are you looking forward to the most? Fractured Peaks for me. 
Just incase you missed this one.
Where ever you want. There may be a starting intro scenario that introduces the current situation then have you off on your way to where ever you want. As of now zones scale to level and you pick which zone campaign(Act) you want to tackle first.
Thus far, no such information such as our starting point had been given out (as far as I know of). However since the campaign is designed around the 5 regions and we can go through said regions in any order; I’d assume that the starting point is either somewhere where it’s easy to reach most if not all of the regions or after creating our characters, we’re given an option to select our starting point and to work from there.
That said, I’ll definitely be looking forward to the Hawezar region as that giant serpentine creature in the gameplay trailer sold it for me (of course, that’s assuming that was the Hawezar region). Regardless, I’ll mostly be looking forward to exploring the world itself, as given Blizzard’s statement on the Diablo 4 world, the world itself promises to be vast one, so taking the time to explore it would be a treat in itself for me.
This is probably the biggest thing I’m excited about.
Hawezar is so deadly, the fauna is ravenous for your flesh, the floor is poisonous. This is a place of madness, of black magic. Who can tell how much of what you see is real, or just some kind of fever dream? Those that come to Hawezar, they do so to be forgotten, to be lost. They are cutthroats, thieves, assassins, murderers that want to do their dark trades far out of the reach of the forces of like law and order, or groups like the Zakarum who might be able to put a stop to this.
This is also the location where we have groups of swamp witches who worship massive snakes, if you saw the gameplay trailer you might have caught a glimpse of one of them. They have dark knowledge, they may be willing to part with, but for a heavy price. - Harrison Pink, Blizzcon
Yep that’s what I’m looking forward to.
This might be interesting if it is an option for use in the game, and not just some NPCs talking to each other.
That may infer that we could either join with certain factions (npc-based factions, not player-based) in the game and gain some unique benefits and/or skills, or complete some unique quests that would grant us said unique benefits. That said, there’d probably be a limit to how many factions we could join and/or how many such unique quests we could complete (assuming either of these are the case).
Factions make sense. We’ve basically been helping them since D2.
I don’t remember where I got the idea, but I seem to remember somewhere reading that each class will start in their own area. For example you have the druids of Scosglen and they will start there. I wish I could remember where I heard that. Maybe I’m just making it up. But having 5 zones and 5 classes seems convenient for that to be true.
If I am right, I hope that doesn’t mean the world will scale with you like it does in Diablo 3. I like areas having levels to them so you can go somewhere harder or easier based on your build and not just changing the difficulty of the game.