So in this game are you still only the one character? I was hoping to see a return to the team of 3 or 4 like FF 7,8,9...
You only play as Noctis - this is how it is in the demo, and as far as I know how the rest of the game will play out. I also miss the party system from the previous games

Type-0 has the opposite approach, giving you 14 characters you can play as!
FF XIII was a real disappointment for me, please tell me XV isn't a linear game like XIII?
Square listened - the demo (and from what I understand, the whole game) is way more open. Think Dragon Age Inquisition - that's what it felt like. The quality of the side quests and such are yet to be seen, but I think it's going to be awesome.
Also how to the skills work? Do you get upgrade points? Or is there a skill tree?
There were no skill upgrades in the demo - they were specifically scratched out "Skills cannot be developed in Final Fantasy XV Episode Duscae". Skills are tied to your weapons, and weapons have 'tiers', on top of your character levels.
After battle, you gain EXP (which is boosted by your performance), and all levelling and upgrades take place when you camp. I'm not sure how skill development will take place, but I know it will happen then, and it will be tied to your new weapons. New weapons will give new skills etc etc.
And no chance of a junction magic feature? One of the reasons why i love FF VIII so much...
Magic was also left out of the demo (apparently it isn't quite ready to show off) - but the demo did show of one summon, and it was seriously boner-inducing. I don't think it will junction-based, I think SE left that behind with FFVIII - I suspect Noctis will be able to use magic associated with whichever summon he has 'equipped', but that's just speculation.