TL;DR: As the DM, I want to prepare my group of newbie friends for the best first experience I can give them. I'm concerned about halts to give explanations ruining the flow of the game and negatively affecting immersion in the story. I thought I might have them play short one-shots in various settings against different events, unrelated to the campaign, instead of letting them dive into it and tailoring the beginning around their inexperience.
This question might sound too broad, so please allow me to clarify. I'm the only experienced player and my closest group of friends has asked me to DM a campaign for them, as they'd love to play D&D all together. However, they are concerned about not being able to follow the huge block of rules and have asked for guidance (to which I said "just read the spell description"... Alright, sorry). They are all completely new to D&D and have never played a RPG before. I'm concerned about them being unable to handle a situation and me being forced to halt the session to give explanations, disrupting the flow and pace of the game and negatively affecting the immersion in the setting. However, perhaps making mistakes through the main story and seeing how they could be relevant in the future might be more instructive.
I'm already intervening on the building of their characters, while also helping them interwine their backstories with the lore of the world and giving support with the definition of their role in the party and the main storyline. I don't want to Pontius-Pilate the issue of mechanics knowledge by saying "read the Handbook, then we'll start when you're all done", as the one they look up to have a fun first experience. They asked to be taught about how they are supposed to act in-game (e.g., "Rather than asking to roll on Investigation to look for a hidden door, tell me how Barendur feels this room isn't all there is and starts touching the wall on the right...").
They feel like they need some sort of preparation, a "warm-up" before diving into the main game, and so do I. Aside from the classical Session 0, I've thought about different "one-shot situations" unrelated to the storyline to put their characters into, to help them better understand what they are supposed to do, what my role is and how the events unfold, e.g. "you're walking through a forest at dusk guided by your Ranger, heading towards the nearest village you know of, to ask for shelter after a long journey...", "you're in a tavern, sitting at a table sipping a hot soup. Suddenly, the guards break into the building, yelling and pointing at what looks like, at first sight from your distant table, a harmless civilian...", and some combat situations.
Do you think this is a good approach? If yes, what should I focus on? If no, then should I just start with the main story, carefully adapting the beginning to the players' inexperience while correcting and adjusting things on the way?
P.S. Perhaps I'm just worrying too much. I really want their first time playing D&D to be the funniest experience I can offer. If this is still too broad and generic, I'm very sorry, please feel free to point it out and I'll delete the question.