I would like to create a game as a skyrim mod, featuring a new landmass (most probably smaller than skyrim), own quests etc.

Is that even possible?

If yes, could someone do a tutorial? I have worked with the creation kit for soe time, i know how to create a dungeon, and how to bring it into skyrim. But I don't know how to create a game (let's call it a microgame for now), with it's own landmass, charaktercreation etc.

Here's what i've been thinking of:
An argonian and the player explore a dungeon. As they cross a plank, the player slipps and falls down a shaft. The game starts with him hearing a voice, asking if he's still alive. He is and opens his eyes. He is barely able to stand, but after some time he gets up. His (or her?!) comrade explains the situation. After getting asked if he still knows who he is, the player beginns the charakter creation. (or, for a start, i might go with a predefined charakter) Then the comrade lowers a rope, but slipps, too, and dies. The player needs to find a way through the dungeon to another exit. The microgame would end here (and would't feature charakter creation), later i would ad the main land and all the stuff.

So. What do I need?
1. Creating a new game: I tell the starter to load the mod and then, if i start a new game, i ge my game, not skyrim.
2. Triggering charakter creation, predefining charakters, making changes to charCreat.
3. Creating a landmass. (Later)

Well, seems I got some ambitions. I hope I can do it.

Yours,
Tloxal

Yes it's possible, but there is a HUGE amount of stuff that goes into it. I've been working on a mod for a new landmass that's only about a third the size of Skyrim, and it's taken me about 16 months and THOUSANDS of hours so far, so don't get into this if you are at all serious about finishing it unless you literally have a HUGE amount of freetime over the next like, two years to do this.

Total conversions are super tough to do and even tougher to do well. You do indeed have some extreme ambitions. So ask yourself, do you really want to finish this? If so, I recommend starting smaller. I modded for almost three years before I even considered my new landmass, and it's still taken a huge amount of time and effort. If you just want to mess around and create a new landmass for funsies, then by all means go ahead. It really depends on what you expect to get out of this.