I'm not too familiar with 5e, but I am with other versions, and I think its safe too say there are some overarching themes, and a few things I have utilized in my own experiences.
Session Zero and Character Creation
Now, when I first started, I never did a session zero. We planned a day to play and we'd spend 3/4th of it making characters. It sucked. Session zero is a great way to do a few things before making characters and playing:
Establish setting: What's the area like that you are playing in? What are key places and key events the average person would know? Where do the characters start their adventure (you dont have to tell them this part unless you want to, but i recommend it)
Establish tone: lighthearded or serious? Let your players know exactly how the game will be so they can plan accordingly
Establish current events: What's going on in the world right now regarding politics and warfare. Just give information the average inhabitant of the land will know.
Then, after you establish this, you can go on to character creation. I HIGHLY recommend making your own. Presets are ok on short adventures, but if you're doing a campaign, go with creation.
Why create characters?
Presets can be dull. They all fit into one cliche or another and its harder for players to grow attached. The greatest memories I have of D&D are insane characters doing equally insane acts. If you tell people to make characters a week in advance and skype each of them to help them out, you'll all be ready to play on game day.
Creating Characters efficiently
mostly, this takes time to master, but a good way to do this in the beginning is to find a niche. Learn a class. Races you can swap for more interesting stuff, because that doesn't require you to learn too much more. Play a class until you get a feel, and it will be easier each time to make the character, knowing what works and what doesn't.
This is one of the hardest things to do, because you can't do too much or too little, otherwise it all comes crashing down. If its a game i plan to do from level 1-30, I plan for multiple storylines, usually about 3. If you decide they're going to kill Demogorgon at the end, no matter what and base all of your planning leading up to that, the players feel gated in their ability to choose. The world of D&D has so many great enemies and adventures. Get a rough outline of about 3. At the beginning, let them choose what to do. Based on the path they take, lead that down one of the larger 3 campaigns and archive the other 2. The problem with planning however is:
THE PLAYERS NEVER DO WHAT YOU PLANNED
it is the golden rule.
Know Your Players
While planning is the hardest, this is the most important. From what i read, your party likes to be able to choose their own path and to have meaningful impact in the party. Maybe a rogue felt bad since he couldnt kill all the goblins like the wizard. How do you counter this? Add in dangerous traps that only the rogue can disarm. Tailor key aspects of your adventure to highlight the strengths of all of the players. With combat, this can be easy too. By choosing the right enemy, with the right weaknesses and strengths, you can play off of the strengths/weaknesses of the players.
Chances are, there's at least one player that likes to be basked in immersion. From the sounds of it, that's you, but probably the others too. Encourage the dwarf to talk in a hilarious Swedish accent while requesting a mead. Encourage the players to describe their attacks. "I bring my blade crashing down on the orc with the fury of the gods, using ___" Sounds so much cooler than "I use ____" Of course, this is on you more than anyone, as the DM. Describing their surroundings and the precise looks of their enemies is one of the most subtle but effective ways of doing this. Appeal to all of their senses, or as many as you can.
**Don't Be a Stickler For The Rules"
I am NOT saying don't learn the rules. You should absolutely, but the thing is, when you first start out, especially if you didn't have a great time in the past, play a lose game. Let people learn at their own pace. As time progresses, you can gradually implement the more minute of details. Of course, still play by the base rules, but if there's a detail you aren't sure on which the fate of the party is riding on, just throw them a bone and they'll appreciate it
Well, I already gave a golden rule, but this is like the platinum rule. Its mentioned in practically every book. Don't say no. If they want to do something cool, not gamebreaking, but cool, just let them do it.. They'll be immersed, they'll have a blast, and everyone wins. Now, don't let them do it all the time, and don't always say absolutely yes, that's where the "but..." comes in. Some things are just too OP and sometimes you have to regulate it with a drawback to stem from it.
In the beginning, its best not to let them make up their own races/classes. I know this isn't something you brought up, but in the future, someone will probably ask. If you can find some races online, they are usually not completely broken, but you should definitely compare them to the standard races. Classes are even harder. I say, stick away from it, even if its from online. Its just too much work to check every aspect for fairness. What you can do though is allow for aesthetic changes.
I know this is 5e, but I'm going to use an example from one of my 4e games. One player wanted to play a runepriest. Basically, they are people who learn the runes of the gods and utilize them to protect, support and destroy. They noted in the book, it said that there were many languages of runes, but the runepriests learn that of the gods. Being a Lovecraft fan, the player wanted to have a dark runepriest who learned the runes of primordials rather than gods. So what did I say?
"Yes, but it will only be an aesthetic change for your character and their spells. Also, while it may open up interesting paths for quests, there's a possibility some people will not accept you."
Its a great character idea, it helps you with quest ideas, it encourages roleplaying and everybody is happy.
HAVE FUN AND DON'T GET CAUGHT UP ON ANYTHING THAT ISN'T