[Update] 1st session: I'm going to bullet point this so it's easier:
1- The party is composed of 3 players with barely any experience and 2 experienced ones. Everyone arrived with their character sheets ready, except the player that wanted to play a dragonborn warlock... I spent almost 3 hours on skype with the rogue ( one of the 3 that had 0 exp playing dnd) making his character sheet and explaining every single lart of it. The Db warlock, even though I reached out to him 6 or 7 times before the session, never really asked me about anything relevant, only why there was no "mana". How can I make clear I want the to arrive with the bare minimum prep, and not sound like an ahole? I feel that taking 2 hours from everybody is really disrespectful.
2- the adventure itself went pretty well. The role play took most of the time, the 2 encounters they had were too easy ( I was a little too forgiving, didn't know how the new players would behave). I fudged an 18 roll for the 7 kobolds in the 1st encounter, cause I felt they might kill some of the players, before they had a chance to have a little fun.
3- after speaking with one of the other players, I feel like I made the following mistakes: 3.1- I was too hard on 1 rolls, with severe punishment for both PC and NPC's. The rogue rolled a 1 while shooting with his Short bow, while his friend were directly between him and the enemies. i made him roll a % and he rolled an 86, so I said that he hit both his friend on the back and almost killed them. How should I approach situations like these? I did something similar when one of my kbolds rolled a 1. 3.2- He also felt like I stream lined the story a bit too much. Considering the party really only had 2 encounters and they just arrived on their 1st city, there wasn't much room for decision making. They loved my story line, the minion selection were all relevant, they loved my custom created pyromancers and the npc's were great(according to him). But when one of the newer players(1st timer) tried to get in a fight against 30 guards, I advised against it. How can I make him see that its not a good idea, balancing decision making freedom and punishment, without "scaring" him from thinking freely? I also did reward bold actions, like when to rogue sneaked past 2 guards, got in a tent, so I let him steal an important gem from the noble in the tent(pretty much made it up there, wasn't in my story). I just felt the other player was doing whatever(getting in a fight in the 1st min of the adventure). Basically how it the best way to say no without saying no lol.
So all in all, I felt things did go pretty well. XD Your advice so far has been great, I am very grateful to everyone that gave some feedback!!!
TL;DR
1- How to make someone know his spells/prepare without being too harsh on him? 2- Make encounters harder? Let some of the players faint if necessary? 3.1- How to deal with 1 rolls? 3.2 - How to let people do unexpected things, while punishing appropriately dumb decisions?